No.  2 


Nt.1 


RULES. 

To  Convert  a  Correct  Magnetic  into  a  Compass  Course. 

A  LLOW  Westerly  Deviation  around  the  Compass  in  the  direction  indicated  by  Hand  No.  2. 
A  LLOW  Easterly  Deviation  around  the  Compass  in  the  direction  indicated  by  Hand  No.  1. 

To  Convert  a  True  Course  into  a  Compass  Course. 

ALLOW  Westerly  Variation  and  Westerly  Deviation  around  the  Compass  in  the  Direction  indicated 
by  Hand  No.  2. 

ALLOW  Easterly  Variation  and  Easterly  Deviation  around  the  Compass  in  the  Direction  indicated 
by  Hand  No.  1. 

To  Convert  a  Compass  Course  into  a  True  Course. 

ALLOW  Leeway  made  on  the  Starboard  Tack,  also  Westerly  Variation  and   Westerly  Deviation* 
around  the  Compass  in  the  direction  indicated  by  Hand  No.  1. 

ALLOW  Leeway  made  on  the  Port  Tack,  also  Easterly  Variation  and  Easterly  Deviation,  around  the 
Compass  in  the  Direction  indicated  by  Hand  No.  2. 

To  Allow  for  Deviation  when  Working  Cross  Bearings. 

TO  CONVERT  a  Compass  Bearing  into  a  Correct  Magnetic  Bearing,  allow  Westerly  Deviation  around 
the  Compass  in  the  Direction  indicated  by  Hand  No.  1. 

TO  CONVERT  a  Compass  Bearing  into  a  Correct  Magnetic  Bearing,  allow  Easterly  Deviation  around 
the  Compass  in  the  Direction  indicated  by  Hand  No.  2. 

Note.    Deviation  is  always  selected  from  Ike  deviation  card  for  the  direction  of  the 
ship's  head  at  the  time  the  bearings  were  taken,  and  not  for  the  bearings  themselves. 

To  Determine  Deviation  by  Terrestrial  Range. 

DEFER  to  the  compass  card  the  correct  magnetic  range  bearing  as  given  by  chart  compass,  also  the 
*^  bearing  of  the  range  as  given  by  the  ship's  compass,  and  if  they  agree  it  proves  that  deviation  is  ab- 
sent on  the  course  headed  at  the  time  of  bearing  ;  but  if  the  correct  magnetic  range  is  on  the  left  hand 
of  the  other  then  the  deviation  is  westerly,  and  if  on  the  right  hand  it  is  easterly. 

To  Determine  Deviation  by  Pole  Star  Bearings. 

f\BSERVE  on  the  chart  the  line  of  compass  variation  passing  through  the  ship's  position,  then  accord- 
*  ' 


^^ 


, 

ing  to  this,  mark  on  the  card*  diagram  how  the  Pole  Star  should  bear  by  the  ship's  compass  if  devi- 
ation did  not  exist.  Next  take  a  bearing  of  the  Star  by  the  ship's  compass,  and  refer  this  bearing  to  the 
card.  Then  if  there  is  no  difference  between  the  two  points,  it  may  be  understood  that  deviation  is 
absent  for  the  ship's  head  ;  but  if  the  compass  bearing  of  the  Star  is  to  the  left  hand  of  the  other,  the 
deviation  is  easterly,  and  if  the  compass  bearing  is  to  the  right  hand  it  is  westerly. 

Solving  Compass  Problems  by  the  Revolving  Card. 

TN  WORKING  OUT  compass  problems  by  the  revolving  card,  the  navigator  may  consider  the  under- 
A  neath  card  as  true,  or  as  correct  magnetic,  and  the  top  card  as  the  ship's  compass,  etc.,  then  by  turning 
the  north  point  of  the  top  card  to  the  right  or  to  the  left  of  the  north  point  of  the  under  card,  as  called 
for,  a  graphic  solution  of  the  problem  will  be  shown. 


THE 

NAVIGATOR'S  POCKET-BOOK 


THE 

NAVIGATOR'S  POCKET-BOOK 

ARRANGED     FOR     IMMEDIATE     REFERENCE     TO     ANY 
NAVIGATION     SUBJECT 

A  Complete  Guide  and  Instructor  for  the  Navigator,  containing  Four 

Hundred  Adequate  Definitions  in  Addition  to  all  the  Practical  Rules 

for  "\Vorking  Middle    Latitude,    Mercatqr's   and  Great  Circle 

Sailings,   as  well  as    Finding  the   Ship's   Place   by  Nu- 

merous Chart  Considerations,  and  the  Latitude  and 

Longitude  by  Dead  Reckoning,  and  by  the 

Sun,  Moon,  Planets,  and  Stars 

ACCORDING   TO    SHORT,    SIMPLE,    AND    RELIABLE    METHODS 

Also  the  Arithmetic  of  Angular  and  Time  Measure 
Compass  Deviation,  Nautical  Astronomy 

Treatise  on  the  Instruments  of  Navigation 
Law  of  Storms,  Keeping  the  Log  Book 

Magnetism,  Logarithms,  Measuring  Altitudes 
Sumner's  Method,  Time,  Weather,  etc.,  etc. 

TOGETHER    WITH    DANGER-ANGLE    AND    OTHER    TABLES 

BY 

CAPTAIN  HOWARD  PATTERSON 


Formerly   U.   S.   Navy;   Commander   of   the   New    York   Schoolship    "St. 
Mary's,"  and  Admiral  of  the  Haytien  Navy 

AUTHOR  OF 

"Patterson's  Illustrated  Nautical  Encyclopedia,"  "Handbook  for  Masters 
and  Mates,"  "Patterson's  Yachting  Series,"  etc. 


YORK 

CHARLES  SCRIBNER'S  SONS 

1917 


VK'rrr 

T3 


Astron. 


COPYBIGHT,  1894,  1903, 
CHARLES  SCRIBNER'S  SON! 


Co 

CHESTER   W.    CHAPIN,    ESQ. 
CORINTHIAN  YACHTSMAN 

Steady  at  the  helm  from  whatever  quarter  comes  the  wind 
Quick  to  catch  either  the  caressing  or  threatening  whisperings  of  the  sea 
And  novice  in  nothing  that  makes  a  sailor  of  the  highest  and  truest 
American  type 

THIS   BOOK    IS   RESPECTFULLY   DEDICATED 
BY   HIS   FRIEND 

THE  AUTHOR 


3G0371 


PREFACE 

THERE  are  many  voluminous  and  bewildering  works  on  the 
subject  of  navigation,  but  up  to  the  present  time  there  has  not 
existed  a  series  of  short,  simple  laws  founded  on  correct  princi- 
ples and  expressed  in  homely  language,  whereby  the  navigator 
might  quickly  develop  his  position  under  various  conditions  at 
sea  and  along  shore.  In  this  little  volume  has  been  incorpo- 
rated every  practical  formula  for  determining  the  latitude  and 
longitude  by  dead  reckoning  and  by  solar,  lunar,  and  stellar 
observations,  as  well  as  concise  and  lucid  directions  for  chart- 
work,  the  various  sailings,  and  for  accurately  fixing  the  ship's 
place  when  in  sight  of  land,  and  in  every  consideration  the 
author  has  succeeded  in  simplifying  and  abridging  the  confus- 
ing and  tedious  rules  and  methods  in  common  use.  The  purely 
original  arrangement  of  .this  pocket  edition  of  common-sense 
navigation  contributes  generously  to  its  value,  as  it  affords  means 
of  immediate  recourse  to  any  and  every  subject  within  the 
sphere  of  the  practical  navigator.  The  problems  are  all  worked 
according  to  Bowditch's  American  Nautical  Tables,  which  may 
be  purchased  from  any  book-dealer  for  $1.25,  but  it  is  to 
be  explained  that  the  numbers  called  for  in  the  text  may  be 


Vlll  PREFACE 

changed  to  apply  to  other  navigation  tables.  In  no  particular, 
has  it  been  attempted  to  go  beyond  the  limits  of  honest,  service- 
able navigation  as  practised  at  sea,  consequently  the  reader 
would  seek  in  vain  for  fancy  or  abstruse  sailings  and  irrelevant 
definitions. 

E.  P. 
NEW  YORK,  1894. 


FOB   1XPLANATION    OF    PARTS   BEX    "SEXTANT.1' 


THE  NAVIGATOR'S  POCKET-BOOK 


A.  M. — Ante  Meridiem  ;  before  meridian  ;  embraces  the 
twelve  hours  from  midnight  to  noon. 

ABOVE  THE  POLE — When  the  north  star  is  situated  so 
that  it  is  intercepted  between  the  observer  and  the  pole,  it  is  said 
to  be  above  the  pole.  This  applies  to  other  circumpolar  bodies. 
(See  Upper  Transit.) 

ADJUSTING  SCREWS.-(See  Sextant.) 

ADJUSTMENT. — The  correction  of  a  compass  for  deviation 
by  the  employment  of  magnets,  or  the  regulation  of  the  mirrors 
of  a  sextant.  (See  Compass  Adjusting ;  Sextant.) 

ALIDADE. — An  instrument  for  taking  bearings,  consisting 
of  two  arms  revolving  around  a  circular  brass  plate  or  dial 
marked  with  the  points  and  degrees  of  the  compass.  It  is 
secured  on  top  of  the  binnacle  hood  and  set  to  the  ship's 
course,  so  that  any  bearing  given  by  it  will  represent  the  mag- 
netic bearing  as  by  the  compass  beneath.  (See  Azimuth 
Attachment ;  Pelorus. ) 

ALMANAC.— A  nautical  calendar  in  which  is  tabulated  for 
the  various  days  of  the  month,  the  declinations  of  the  sun, 
moon,  planets  and  stars  ;  their  right  ascensions  ;  the  equation  of 
time,  etc. 


2  THE  NAVIGATOR'S  POCKET-BOOK 

ALTITUDE. — The  acgula?  height  of  a  body  above  the 
horizon. 

Remarks  Concerning  Meridian  Altitudes. — The  term  me- 
ridian altitude  means  the  highest  point  attained  by  a  heavenly 
body  above  the  observer's  horizon,  which  is  secured  when  the 
object  bears  either  true  north  or  south  as  the  case  may  be. 
When  the  observer  is  north  of  the  body's  declination  it  will  be 
observed  to  the  south,  but  when  the  observer  is  south  of  the 
body's  declination  its  image  will  be  thrown  to  the  northern 
horizon. 

By  mentally  adding  four  minutes  of  time  to  the  face  of  the 
ship's  clock  for  every  degree  of  longitude  sailed  east  since  the 
clock  was  last  set,  or  subtracting  four  minutes  for  every  degree 
sailed  west,  the  observer  will  be  enabled  to  anticipate  the  time 
of  the  meridian  passage  and  be  prepared  to  observe  the  same. 

There  are  two  methods  employed  for  bringing  the  image  of  a 
heavenly  body  to  the  horizon  at  the  time  of  the  meridian  pas- 
sage, the  first  of  which  is  as  follows  : 

Make  the  vernier  and  arc  zeros  cut  one  another,  then,  in  the 
case  of  the  sun,  turn  down  the  shade-glasses  to  suit  the  eye  ; 
point  the  telescope  toward  the  body  so  that  its  colored  image  is 
seen  in  the  horizon-glass  ;  now  advance  the  sliding  limb,  and  in 
proportion  as  it  is  moved  along  the  arc,  bring  the  sextant  to  the 
vertical — otherwise  the  image  would  disappear  from  the  horizon- 


The  second  method  practised  oftentimes  at  sea  for  the  me- 
ridian observation  is  to  anticipate  the  approximate  altitude 
and  to  set  the  same  on  the  sextant,  then  to  direct  the  telescope 
to  that  part  of  the  horizon  which  is  beneath  the  body,  making  a 
perfect  contact  by  the  aid  of  the  tangent  screw.  This  latter 
method  obviates  the  necessity  of  "  shooting  the  heavens"  and 


THE  NAVIGATOR'S  POCKET-BOOK  3 

insures  against  blinding  from  the  dazzling  effects  of  the  sun 
when  caught  in  the  unsilvered  part  of  the  horizon-glass.  To 
calculate  the  approximate  altitude,  proceed  as  follows : 

When  the  latitude  by  dead-reckoning  and  the  declination  of 
the  body  are  of  the  same  name,  subtract  them  from  one  another, 
then  subtract  the  remainder  from  90°— the  answer  will  be  the 
approximate  altitude. 

When  the  latitude  by  dead-reckoning  and  the  declination  of 
the  body  are  of  contrary  names,  add  them  together,  then  sub- 
tract their  sum  from  90° — the  answer  will  be  the  approximate 
altitude. 

A  meridian  altitude  will  always  be  some  part  of  90°— an  arc 
from  the  horizon  to  the  point  directly  over  the  head  of  the  ob- 
server, called  the  zenith.  This  arc  is  always  a  quadrant  (90°), 
and  what  an  altitude  lacks  of  90°  is  always  the  zenith  distance. 

Meridian  Altitude  of  the  Sun.— Considering  that  the  sun's 
image  has  been  brought  almost  in  contact  with  the  horizon, 
proceed  to  make  a  perfect  contact  by  the  aid  of  the  tangent 
screw,  fingering  the  same  until  the  sun's  lower  limb  is  just  kiss- 
ing the  horizon  line.  The  vertical  movement  of  this  luminary 
is  very  slow  when  approaching  the  meridian,  and  within  several 
minutes  of  noon  on  each  side  of  that  point  its  motion  is  imper- 
ceptible. Until,  however,  the  body  is  almost  on  the  observer's 
meridian  its  limb  will  show  a  slow  but  steady  lifting  above  the 
horizon,  and  must  be  brought  down  when  it  shows  daylight  be- 
tween it  and  that  part  of  the  horizon  which  is  directly  beneath. 
The  idea  is  to  secure  the  highest  altitude  which  the  sun  offers. 

In  order  to  be  positive  of  the  proper  place  of  contact,  the 
navigator  should  oscillate  (swing)  the  instrument  while  keeping 
the  eye  to  the  telescope,  so  that  the  sun's  image  will  appear  to 
describe  the  lower  segment  of  a  circle,  the  lowest  point  of 


4  THE   KAVIGATOll's    POCKET-BOOK 

which  will  be  the  horizon  directly  beneath  the  sun,  ana  to 
which  point  the  limb  of  the  sun  must  be  brought  in  contact. 

As  soon  as  it  is  decided  that  the  sun  is  done  rising,  call  "  eight 
bells  ! "  The  hands  of  the  ship's  clock  will  then  be  set  at  twelve, 
as  the  apparent  or  sun  time  at  the  ship.  Although  twelve 
o'clock  has  been  "  made  "  at  ship,  do  not  consider  the  observa- 
tion finished  until  the  image  of  the  sun's  limb  is  seen  to  dip 
below  the  horizon  line  ;  but  when  this  is  observed,  under  no 
circumstances  bring  the  sun's  limb  up  to  the  line  of  the  horizon, 
as  the  dipping  of  the  limb  proves  that  the  body  has  crossed  over 
the  highest  point  of  the  great  circle  which  it  describes  from 
rising  to  setting ;  and  it  is  from  this  highest  altitude  that  we 
must  calculate  the  ship's  distance  from  the  equator  by  the  appli- 
cation of  the  declination. 

In  relation  to  the  use  of  the  upper  and  lower  limbs  of  the  sun 
when  observing  its  altitude,  it  will  be  found  that  the  lower 
limb  will  afford  the  most  satisfactory  result,  as  a  daylight  line 
may  be  distinguished  between  it  and  the  horizon  ;  whereas  the 
sinking  of  the  upper  limb  to  the  horizon  is  attended  with  danger 
of  inaccuracy.  (See  Latitude.) 

Ex.  Meridian  Altitude  of  the  Sun — This  altitude  is  meas- 
ured by  simply  bringing  the  sun's  image  down  to  that  part  of  the 
horizon  line  that  is  directly  beneath  the  body,  proving  the  point 
of  contact  by  the  oscillation  of  the  sextant.  Without  further 
consideration  or  delay  the  measured  altitude  is  accepted  and  read. 

Time  Altitude  of  the  Sun.— When  observing  an  altitude  of 
the  sun  for  finding  the  longitude  by  a  chronometer  sight  or  by 
equal  altitudes,  simply  throw  the  sun's  image  to  that  part  of  the 
horizon  which  is  directly  beneath  the  body,  proving  the  point  of 
contact  by  oscillating  the  sextant,  and  at  the  instant  of  proper 
contact  note  the  Greenwich  hour,  minute,  and  second  shown 


THE  NAVIGATOR'S  POCKET-BOOK  5 

by  the  chronometer.  This  may  be  done  by  having  some  one 
stationed  by  the  time-piece,  who  will  make  a  memorandum  of 
the  time  when  so  directed  by  the  navigator  calling  "time" 
when  he  brings  the  sun's  limb  in  perfect  contact,  or  it  may  also 
be  done  by  the  navigator  himself  having  a  hack  watch  set  to 
Greenwich  time  which  he  holds  in  the  hollow  of  his  left  hand, 
with  its  face  toward  him,  so  that  it  is  in  plain  view  while 
measuring  the  altitude.  (See  Longitude.) 

Altitudes  in  Foggy  Weather.— When,  owing  to  light  fog  or 
mist,  the  radius  of  the  visible  horizon  is  only  two  or  three  miles, 
get  the  eye  as  near  to  the  surface  of  the  water  as  possible  when 
measuring  the  altitude  of  a  heavenly  body,  and  by  this  means 
the  horizon  may  often  be  brought  within  the  fog-described 
circle.  Should  the  fog  be  heavy,  it  may  be  possible  to  get  above 
it  by  going  aloft.  When  this  can  be  accomplished  a  good  obser- 
vation is  obtainable. 

Altitudes  in  Cloudy  Weather. — When  the  mass  of  the  sun 
or  moon  is  visible,  but  the  limbs  ill-defined  in  consequence  of  an 
overcast  sky  or  the  body  shining  through  a  rain-cloud  or  light 
fog,  the  image  of  the  mass  may  be  brought  down  and  the  centre 
of  this  ball  of  light  calculated  and  allowed  to  be  cut  by  the 
horizon  line.  In  this  case  no  allowance  is  to  be  made  for 
semi-diameter.  The  ship's  position,  determined  by  this  method, 
will  probably  be  a  little  in  error,  but  as  a  makeshift  the  rule  has 
its  value. 

Meridian  Altitude  of  the  Moon. — The  astronomical  mean 
time  of  the  moon's  meridian  passage  is  given  in  the  nautical 
almanac  for  everyday  of  the  month  at  Greenwich,  and  this  time 
answers,  within  a  few  minutes,  for  all  longitudes.  Proceed  to 
observe  the  altitude  in  the  same  manner  as  explained  for  the  sun, 
out  use  no  shade-glasses.  If  the  horns  of  the  moon  are  down  it 


6  THE  JSTAVIGATOR'S  POCKET-BOOK 

will  be  necessary  to  measure  the  altitude  of  the  upper  limb  ;  but 
if  the  horns  are  up  the  lower  lirnb  will  be  measured.  When  the 
moon  is  full,  or  nearly  so,  measure  the  lower  limb  always  in 
preference  to  the  upper  limb.  (See  Latitude.) 

Time  Altitude  of  the  Moon. — This  is  observed  in  exactly  the 
same  manner  as  described  for  a  time  altitude  of  the  sun,  omit- 
ting the  shade-glasses  and  having  regard  to  the  upper  and  lower 
limbs  as  explained  in  Meridian  Altitude  of  the  Moon.  (See 
Longitude.) 

Meridian  Altitude  of  a  Planet. — The  astronomical  mean 
times  of  the  meridian  passages  of  the  planets  are  given  in  the 
nautical  almanac  for  every  day  of  the  month,  and  apply  prac- 
tically to  all  longitudes.  Proceed  in  precisely  the  same  way  as 
explained  for  a  meridian  sight  of  the  sun,  but  use  no  shade- 
glasses  and  do  not  take  the  semi-diameter  into  consideration. 
(See  Latitude.) 

Time  Altitude  of  a  Flanet.-^This  is  observed  in  exactly  the 
same  manner  as  described  for  a  time  altitude  of  the  sun,  omit- 
ting, of  course,  the  shade-glasses.  (See  Longitude.) 

Meridian  Altitude  of  a  Star. — The  following  method  of  ap- 
proximating the  star's  altitude  and  placing  the  same  on  the  sex- 
tant should  be  observed,  as  it  insures  against  bringing  down  the 
wrong  body : 

When  the  latitude  by  dead-reckoning  and  the  star's  declina- 
tion are  of  the  same  name,  subtract  them  from  one  another,  then 
subtract  the  remainder  from  90° — the  answer  will  be  the  rough 
altitude ;  but  when  the  latitude  by  dead-reckoning  and  the 
star's  declination  are  of  contrary  names,  add  them  together  and 
subtract  their  sum  from  90° — the  answer  will  be  the  rough 
altitude. 

A  few  minutes  before  the  time  given  in  the  star  tables  (in  the 


THE  NAVIGATOR'S  POCKET-BOOK  7 

back  of  this  volume)  for  the  meridian  passage,  set  the  sextant, 
direct  it  either  to  the  north  or  south  horizons,  according  to  the 
latitude  of  the  ship  and  the  declination  of  the  body,  and  the 
star's  image  will  be  seen  in  the  horizon-glass  of  the  instrument ; 
then  make  a  perfect  contact  by  the  aid  of  the  tangent  screw,  and 
wait  for  the  star  to  reach  its  highest  point,  proceeding  in  the 
same  manner  as  described  for  a  meridian  observation  of  the  sun, 
it  being  understood  that  shade-glasses  are  not  employed. 

The  declination  of  the  star  as  compared  with  the  latitude  of 
the  ship  will  always  dictate  the  direction  (north  or  south)  in 
which  to  look  for  the  horizon  beneath  the  body.  If  the  star's 
declination  is  north  of  the  ship's  position,  the  northern  horizon 
will  be  used,  but  if  the  star's  declination  is  south  of  the  ship's 
position,  the  southern  horizon  will  be  used. 

Dawn  and  twilight  afford  the  best  horizons  for  star  observa- 
tions. (See  Latitude.) 

Time  Altitude  of  a  Star.— This  is  observed  in  the  same  man- 
ner as  described  for  a  time  altitude  of  the  sun,  only  without 
making  use  of  the  shade-glasses.  It  is  to  be  explained,  how- 
ever, that  until  the  navigator  has  studied  the  heavens  and  be- 
come sufficiently  familiar  with  them  to  locate  the  nautical  stars 
when  they  are  off  the  meridian,  this  method  of  finding  the 
longitude  cannot  be  employed  by  him.  The  superior  size  and 
brilliancy  of  the  planets  will  always  prove  an  unfailing  guide 
when  desiring  to  select  one  of  those  bodies,  but  confusion  will 
at  once  arise  in  seeking  to  fix  upon  particular  stars  unless  the 
observer  is  acquainted  with  their  relative  places.  (See  Fixed 
Stars  ;  Longitude.) 

Altitude  of  the  Pole  Star.— Simply  throw  the  star's  image  to 
that  part  of  the  horizon  which  is  directly  beneath  the  body, 
proving  the  point  of  contact  by  oscillating  the  sextant,  and  note 


8  THE  NAVIGATOR'S  POCKET-BOOK 

the  local  apparent  time  at  ship  as  shown  by  the  clock.  (See 
Latitude.) 

Remarks.—  Under  the  head  of  Sextant  will  be  found  full  and 
practical  directions  for  adjusting  the  instrument  and  reading 
the  altitude.  (See  also  Corrected  Altitude  ;  Quadrant ;  Oc- 
tant.) 

If  the  star  telescope  is  used,  be  particular  to  observe  as  closely 
as  possible  in  the  centre  of  the  field. 

AMPLITUDE. — The  bearing  (never  exceeding  90°)  of  a 
heavenly  body  at  rising  or  setting.  To  ascertain  the  variation 
and  deviation  of  a  compass  by  employing  an  amplitude,  pro- 
ceed as  follows : 

To  Find  the  Magnetic  Amplitude. — Observe  the  sun  to 
rise  or  set  and  note  its  magnetic  bearing  by  the  compass,  pelorus, 
or  alidade,  which  bearing  will  be  named  east  so  many  degrees 
north  or  south  at  rising,  but  west  so  many  degrees  north  or 
south  at  setting,  as  the  case  may  be. 

To  Find  the  True  Amplitude.— With  the  latitude  by  dead- 
reckoning  to  the  nearest  degree,  and  the  sun's  declination  to  the 
nearest  half  degree,  enter  table  39  and  select  the  sun's  true  bear- 
ing, which  will  be  named  north  if  the  declination  is  north,  and 
south  if  the  declination  is  south. 

To  Find  the  Whole  Variation.— The  difference  between  the 
compass  bearing  and  the  true  bearing  (subtracted  if  of  the  same 
name,  but  added  if  of  different  names)  will  be  the  whole  amount 
of  the  compass  variation,  or  the  angle  made  with  the  true  me- 
ridian by  the  compass  needle,  and  it  will  be  named  as  follows  : 

To  Name  the  Variation. — Refer  to  a  compass  card  and  mark 
the  points  representing  the  bearings,  then  imagine  the  eye  in 
the  centre  of  the  compass  looking  at  the  point  standing  for  the 
magnetic  (compass)  bearing,  and  if  the  true  bearing  is  to  the 


THE  NAVIGATOR'S  POCKET-BOOK  9 

right  hand  of  the  magnetic  bearing  the  variation  is  easterly, 
but  if  to  the  left  hand  it  is  westerly. 

To  Find  the  Deviation. — If  the  compass  has  no  deviation, 
then  the  whole  amount  of  the  variation  determined  by  the  am- 
plitude will  agree  with  the  variation  given  by  the  chart  for  the 
ship's  position,  but  if  they  do  not  agree,  their  difference  will  be 
the  deviation  of  the  compass  for  that  particular  course  the  ship 
was  heading  at  the  time  of  the  observation,  and  it  will  be  named 
according  to  the  following  : 

To  Name  the  Deviation. — Suppose  that  the  variation  found 
by  amplitude  is  10°  east,  and  the  variation  given  by  the  chart  is 
5°  west.  Now  as  the  chart  tells  us  that  the  north  point  of  our 
compass  needle  in  order  to  be  correct  magnetic  should  be  in- 
clined 5°  to  the  west  of  the  geographical  or  true  north,  and  we 
find  by  our  observation  that  it  is  inclined  10°  to  the  east,  it  stands 
that  the  compass  has  15°  of  easterly  deviation. 

Again,  suppose  the  variation  found  by  amplitude  is  8°  east, 
and  the  variation  given  by  chart  is  3°  east,  it  shows  that  the  com- 
pass needle  is  deflected  5°  too  much  to  the  east,  hence  easterly 
deviation. 

Once  more,  suppose  that  the  variation  found  by  amplitude  is 
15°  west  and  the  variation  given  by  chart  is  13°  west ;  it  shows 
that  the  compass  needle  has  2°  of  westerly  deviation. 

AMPLITUDE  TABLES. — True  bearings  of  heavenly  bodies 
at  rising  and  setting,  calculated  for  various  latitudes  and  dec- 
linations. 

ANEMOMETER.— An  instrument  that  measures  the  force 
of  the  wind. 

ANEROID  BAROMETER. — An  instrument  that  registers 
atmospheric  pressure,  its  principle  of  construction  being  as  fol- 


10  THE  NAVIGATOR'S  POCKET-BOOK 

lows :  The  weight  of  the  atmosphere  presses  on  a  thin  metal 
box  from  which  the  air  has  been  extracted  and  which  is  kept 
from  collapsing  by  a  spring.  To  this  box  is  secured  by  a  me- 
chanical arrangement  the  index-hand  that  moves  around  the  dial 
or  face  of  the  barometer.  When  the  atmospheric  pressure  in- 
creases a  spring,  acting  on  a  lever,  turns  the  hand  to  the  right, 
and  when  the  pressure  decreases  the  hand  turns  to  the  left.  (See 
Barometer. ) 

ANGLE.— The  divergence  of  two  lines  starting  from  the 
same  point.  (See  Angle  of  Incidence.) 

ANGULAR  DISTANCE.— Measured  by  an  angle  ;  a  certain 
number  of  degrees  of  arc. 

ANNUAL  VARIATION — The  yearly  change  of  the  com- 
pass variation  in  the  same  locality,  or  the  yearly  change  of  dec- 
lination and  right  ascension  tabulated  for  the  fixed  stars. 

ANTARCTIC  CIRCLE.— The  parallel  of  66°  32',  which  di- 
vides the  south  temperate  from  the  south  frigid  zone. 

APPARENT  TIME. — Time  calculated  by  the  sun.  When 
the  sun  crosses  the  meridian  of  the  observer  it  is  apparent  noon 
where  he  is,  as  well  as  at  all  places  on  his  meridian  from  pole  to 
pole. 

ARC. — A  part  of  a  circle.  (See  Diurnal  Arc ;  Nocturnal  Arc  ; 
Sextant.) 

ARCTIC  CIRCLE,— The  parallel  of  66°  32',  which  divides 
the  north  temperate  from  the  north  frigid  zone. 

ARITHMETIC  OP  NAVIGATION.— The  arithmetic  of 
practical  navigation  is  extremely  simple  and  is  included  in  the 
following: 


THE  NAVIGATOR'S  POCKET-BOOK  11 

Angular  Measure. — 

60  seconds  (60")  make  1  minute  (!'). 
60  minutes  (60')  make  1  degree  (1°). 
Time  Measure — 

60  seconds  (60  sec.)  make  1  minute  (1  m.). 
60  minutes  (60  m.)  make  1  hour  (1  h.). 

To  Convert  Time  into  Arc. — Convert  hours,  minutes,  and 
seconds  into  arc  according  to  table  7  or  by  the  following : 
1  hour  is  equal  to  15°,  so  multiply  the  hours  by  15. 
4  m.  is  equal  to  1°,  so  divide  the  minutes  by  4. 
4  sec.  is  equal  to  1',  so  divide  the  seconds  by  4. 
To  Convert  Arc  into  Time.— Multiply  the  longitude  by  4 
and  this  will  turn  the  degrees  of  arc  into  minutes  of  time,  the 
minutes  of  arc  into  seconds  of  time,  and  the  seconds  of  arc  into 
what  is  known  as  thirds  of  time  (a  third  is  the  name  given  to 
the  sixtieth  part  of  a  second).     By  dividing  by  60  these  quanti- 
ties will  be  reduced  to  hours,  minutes,  and  seconds  of  time. 
(See  table  7.) 

Arithmetical  Signs. — 

=  equal  to,  the  sign  of  equality. 
-h  plus,  the  sign  of  addition. 
—  minus,  the  sign  of  subtraction. 
x  multiplied  by,  the  sign  of  multiplication. 
-T-  divided  by,  the  sign  of  division. 
Addition  of  Degrees,  Minutes,  and  Seconds. — 
35°  30'  20"  27°  27'  56" 

20°  20'  30"  36°  57'  49' 

55°  507  50"  64°  25'  45" 

Subtraction  of  Degrees,  Minutes,  and  Seconds. — 
11°  12'  10"  26°  35'  42" 

10°  10'  10*  12°  45f  50" 

1°  02'  00"  13°  49'  52" 


12  THE  NAVIGATOR'S  POCKET-BOOK 

Multiplication  of  Degrees,  Minutes,  and  Seconds. 
10°  10'  10"  13°  59'  58" 

5  3 

50°  50'  50"  41°  59'  54" 

Division  of  Degrees,  Minutes,  and  Seconds. — 
2)40°  20'  10"  2)37°  15'  52* 


20°  10'  05"  18°  37'  56" 
Addition  of  Decimals. — 

6.5  7.9 

5.2  6.9 

3.2  4.9 

14.9  19.7 
Subtraction  of  Decimals. — 

19.7  29.5 

4.3  13.6 

15.4  15.9 
Multiplication  of  Decimals. — 

20.1  15.6 

5  4 

100.5  62.4 
Division  of  Decimals. — 

2)18.4  2)17.6 

9.2  8.8 

ARTIFICIAL  HORIZON.— A  small  trough  filled  with 
quicksilver,  which  latter  is  protected  from  the  ruffling  effects 
of  the  wind  by  a  glass  roof.  It  is  used  on  shore  to  catch  the 
image  of  a  heavenly  body  and  to  measure  its  altitude  for  the 
purpose  of  determining  the  latitude  and  longitude.  A  pan  of 


THE  NAVIGATOR'S  POCKET-BOOK  13 

molasses  or  liquid  tar  has  often  been  employed  with  fairly  good 
results,  in  the  absence  of  a  regular  artificial  horizon. 

The  theory  of  the  artificial  horizon  is  based  upon  the  estab- 
lished principle  that  the  angle  of  reflection  is  equal  to  the  angle 
of  incidence — that  a  ray  of  light  striking  a  plane-reflecting  sur- 
face will  leave  it  at  the  same  angle  precisely. 

Rules. — Place  the  trough  on  firm  ground  and  as  free  from  the 
wind  as  possible  so  that  the  surface  of  the  liquid  may  not  be 
disturbed,  then  face  the  heavenly  body  and  step  backward  until 
its  reflection  is  seen  in  the  quicksilver.  The  image  will  now  be 
brought  down  by  the  sextant  until  it  is  in  contact  with  the  other 
image  in  the  trough,  and  the  angle  shown  on  the  sextant  will  be 
double  the  altitude  of  the  body,  consequently  it  will  be  divided 
by  2. 

When  observing  the  lower  limb  of  the  sun  in  the  morning  the 
images  will  separate,  but  in  the  afternoon  they  will  close. 

In  the  case  of  the  sun,  if  the  nearest  limbs  of  the  two  images 
are  brought  in  contact  half  of  the  angle  obtained  by  the  sextant 
will  be  the  altitude  of  the  lower  limb,  but  if  the  farthest  limbs 
are  brought  in  contact  half  of  the  angle  obtained  will  be  the 
altitude  of  the  upper  limb,  and  the  semi-diameter  will  be  applied 
according  to  the  regular  rules  given  for  the  sun  under  the  head 
of  Corrected  Altitude.  The  sun's  altitude  obtained  must  also 
be  corrected  for  parallax  and  refraction,  but  not  for  dip,  because 
that  quantity  is  eliminated  by  the  use  of  the  artificial  horizon. 

When  ready  to  observe  the  altitude  for  a  time  sight  it  is  best 
to  separate  the  images  or  overlap  them  a  trifle,  as  the  case  may 
require ;  then  wait,  in  the  first  place,  for  them  to  kiss  (close),  or, 
in  the  second  place,  for  the  limbs  to  all  but  part,  and  at  such 
instant  of  perfect  contact  note  the  Greenwich  time  and  proceed 
to  find  the  place  of  the  observer  by  the  given  rules. 


14  THE  NAVIGATOR'S  POCKET-POOK 

Before  observing  an  altitude  the  glass  roof  should  be  carefully 
wiped  clean,  and  if  dust-scum  is  seen  to  rest  on  the  surface  of 
the  mercury  it  should  be  brushed  off. 

When  equal  altitudes  are  observed  be  sure  to  measure  the  same 
limb  in  the  P.M.  that  was  measured  in  the  A.M.  ;  otherwise  the 
result  will  be  unsatisfactory. 

It  is  to  be  explained  that  when  a  heavenly  body  is  much  more 
than  60°  above  the  horizon  it  cannot,  as  a  rule,  be  measured  by 
an  artificial  horizon,  because  on  the  majority  of  sextants  the 
reading  does  not  go  far  above  120°. 

ASTRONOMICAL  DAY. — This  commences  at  noon  of  the 
civil  day,  the  hours  being  counted  numerically  from  1  to  24,  so 
that  the  day  begins  and  ends  at  noon. 

ASTRONOMICAL  TIME.— The  civil  day  begins  at  mid- 
night, twelve  hours  before  the  astronomical  day,  which  com- 
mences at  noon.  To  convert  civil  time  into  astronomical  time 
it  is  only  necessary  to  proceed  as  follows  : 

If  the  civil  time  is  A.M.  take  one  from  the  date  and  add  12  to 
the  hours ;  but  if  the  civil  time  is  P.M.  simply  take  away  the 
sign  P.M.,  and  the  answer  will  be  the  astronomical  time. 

To  change  astronomical  time  into  civil  time,  if  the  hours  are 
less  than  twelve,  simply  write  P.M.  after  them  ;  but  if  the  hours 
are  more  than  twelve  subtract  twelve  hours  from  them,  call  the 
remainder  A.M.,  and  add  1  to  the  days  of  the  month. 

ASTRONOMY.— That  science  which  treats  of  the  heavenly 
bodies,  their  orbits,  distances,  etc. 

AUGMENTED  ALTITUDE.— Increased  altitude  ;  the  cor- 
rection in  arc  added  to  an  ex-meridian  altitude. 

AUTUMNAL  EQUINOX — The  period  of  the  year  when 
the  sun  crosses  the  equator  from  northern  into  southern  declina 


THE  NAVIGATOR'S  POCKET-BOOK  15 

tions.     This  is  known  as  the  First  Point  of  Libra.     (See  Spring 
Equinox.) 

AXIS.— A  line  on  which  a  body  is  supposed  to  revolve. 

AXIS  OP  COLLIMATION.— The  line  of  sight  in  an  instru- 
ment, being  the  line  which  passes  through  the  centre  of  the 
object-glass  and  the  intersection  of  the  wires  placed  in  its  focus. 
What  is  known  as  the  error  of  collimation  is  the  difference 
between  the  actual  line  of  sight  and  the  position  which  that  line 
should  have  in  reference  to  the  axis  of  motion  of  the  instrument. 
Should  the  line  of  sight  of  the  telescope  be  inclined  to  the  plane 
of  the  instrument,  instead  of  perfectly  parallel  to  it,  all  angles 
measured  by  the  sextant  will  be  too  great. 

AZIMUTH. — The  bearing  (never  exceeding  180°)  of  a  heav- 
enly body  calculated  from  the  north  or  south  points  of  the 
heavens.  To  ascertain  the  variation  and  deviation  of  the  com- 
pass by  an  azimuth,  proceed  as  follows : 

To  Find  the  Magnetic  Azimuth  and  Time. — Observe  the 
sun's  bearing  by  compass,  alidade,  or  pelorus,  and  note  the  local 
time  shown  by  the  ship's  clock,  which  latter  correct  by  adding 
to  it  four  minutes  of  time  for  every  degree  of  longitude  sailed 
east  since  the  clock  was  last  set,  but  by  subtracting  four  min- 
utes for  every  degree  sailed  west. 

In  north  latitudes  A.M.  azimuth  bearings  are  counted  north  so 
many  degrees  east,  and  P.M.  azimuth  bearings  are  counted  north 
so  many  degrees  west. 

In  south  latitudes  A.M.  azimuth  bearings  are  counted  south  so 
many  degrees  east,  and  P.M.  azimuth  bearings  are  counted  south 
so  many  degrees  west. 

To  Find  the  True  Azimuth. — With  the  corrected  local  ap- 
parent time  and  the  latitude  of  the  ship  to  the  nearest  degree 


16  THE  NAVIGATOR'S  POCKET-BOOK 

by  dead-reckoning,  also  the  declination  of  the  sun  to  the  nearest 
degree,  enter  the  azimuth  tables  and  select  the  sun's  true  bearing. 

To  Find  the  Whole  Variation. — The  difference  between  the 
compass  and  true  bearings  (always  found  by  subtracting  one 
from  the  other)  will  be  the  whole  amount  of  the  variation  of 
the  compass  needle  from  the  true  north,  and  it  will  be  named  as 
follows  : 

To  Name  the  Variation. — Refer  to  a  compass  card  and  mark 
the  two  points  representing  the  bearings,  then  imagine  the  eye 
in  the  centre  of  the  compass  looking  at  the  point  standing  for 
the  magnetic  (compass)  bearing,  and  if  the  true  bearing  is  to  the 
right  hand  of  the  magnetic  bearing  the  variation  is  easterly,  but 
if  to  the  left  hand,  it  is  westerly. 

To  Find  the  Deviation. — If  the  compass  has  no  deviation, 
then  the  whole  amount  of  the  variation  determined  by  the  azi- 
muth will  agree  with  the  variation  given  by  the  chart  for  the 
ship's  position,  but  if  they  do  not  agree  their  difference  will  be 
the  deviation  of  the  compass  for  that  particular  course  headed 
by  the  ship  at  the  time  of  the  observation,  and  it  will  be  named 
according  to  the  following  : 

To  Name  the  Deviation.— Suppose  that  the  variation  found 
by  azimuth  is  7°  west  and  the  variation  given  by  chart  is  9°  east. 
Now  as  the  chart  tells  us  that  the  north  point  of  our  compass 
needle  in  order  to  point  correct  magnetic  should  be  inclined  9° 
to  the  east  of  the  geographical  or  true  north,  and  we  find  by  our 
observation  that  it  is  inclined  7°  to  the  west,  it  stands  that  the 
compass  has  16°  of  westerly  deviation. 

Again,  suppose  that  the  variation  found  by  azimuth  is  14° 
west  and  the  variation  given  by  chart  is  6°  west :  it  shows  that 
the  compass  needle  is  deflected  8°  too  much  to  the  west,  hence 
westerly  deviation. 


THE  NAVIGATOR'S  POCKET-BOOK  17 

Once  more,  suppose  that  the  variation  found  by  azimuth  is 
20°  east  and  the  variation  given  by  the  chart  is  19°  east  :  it 
proves  that  the  compass  needle  has  1°  of  easterly  deviation. 

AZIMUTH  ATTACHMENT A  small,  portable,  mechani- 
cal device,  consisting  of  two  revolving  arms  or  sight-vanes,  for 
resting  on  the  compass-glass  and  by  which  bearings  are  taken. 
(See  Alidade  ;  Pelorus.) 

AZIMUTH  CIRCLE.— Another  name  for  an  azimuth  at- 
tachment. 

AZIMUTH  COMPASS.— A  portable,  dry -card  compass 
provided  with  sight-vanes  and  used  for  taking  bearings.  It  is 
now  obsolete. 

AZIMUTH  MIRROR.— A  small,  portable  instrument  pro- 
vided with  a  silvered  glass  and  used  for  taking  bearings.  It 
steps  in  a  small,  shallow  hole  bored  in  the  centre  of  the  com- 
pass-glass, and  is  turned  around  until  the  image  of  the  desired 
object  is  seen  in  the  mirror,  when  its  bearing  is  read.  (See  Ali- 
dade ;  Azimuth  Attachment  ;  Pelorus.) 

AZIMUTH  TABLES.— True  bearings  of  the  sun  calculated 
for  various  latitudes,  declinations,  and  times  from  sunrise  to 
sunset. 

BACK  SHADES.— (See  Sextant.) 

BAROMETER. — An  instrument  for  measuring  the  weight 
or  pressure  of  the  atmosphere,  and  sometimes  referred  to  as  a 
weather-glass,  as  it  indicates  the  probable  changes  in  the  weather. 
The  normal  condition  or  average  standing  of  the  barometer  for 
the  sea-level  is  about  thirty  inches.  As  a  rule,  when  the  barom- 
eter continues  steady,  settled  weather  may  be  anticipated  ;  but 
if  it  is  unsteady,  a  change  is  promised.  A  sudden  rise  of  the 


18  THE  NAVIGATOR'S  POCKET-BOOK 

barometer  is  nearly  as  bad  as  a  sucbden  fall,  as  it  proves  that  the 
equilibrium  of  the  atmosphere  is  unsettled.  The  average  range 
(rise  and  fall)  of  the  barometer  in  the  higher  latitudes  is  1.5  (one 
inch  and  five-tenths)  ;  in  the  intertropical  parallels  from  0.2  to 
0.4  (two  to  four-tenths),  and  near  the  equator  only  0.15  (fifteen- 
hundredths  of  an  inch).  In  hurricanes  the  barometer  ranges 
from  1.0  to  2.5  (one  to  two  and  a  half  inches) — the  rapidity  of 
the  fall  increasing  as  the  storm-centre  approaches. 

On  the  mercurial  barometer  the  scale  is  spaced  off  in  inches, 
whence  is  derived  such  terms  as  "the  barometer  stands  at  thirty 
inches,"  etc.,  meaning  in  this  instance  that  the  level  of  the  mer- 
cury in  the  glass  tube  is  opposite  the  thirty-inch  division  of  the 
scale.  (See  Aneroid  Barometer  ;  Mercurial  Barometer  ;  Law  of 
Storms ;  Weather.) 

BASE-LINE. — The  lowest  side  of  a  geometrical  figure  ;  at 
a  right  angle  to  the  perpendicular. 

BEARING. — The  direction  of  one  object  from  another  ac- 
cording to  the  compass.  (See  Alidade  ;  Azimuth  Attachment ; 
Pelorus.) 

BELOW  THE  POLE. — When  the  north  star  is  situated  so 
that  the  pole  is  intercepted  between  it  and  the  observer,  it  is  said 
to  be  below  the  pole.  This  applies  to  other  circumpolar  bodies. 
(See  Latitude  ;  Upper  Transit.) 

BOXING  THE  COMPASS.— (See  Compass.) 

CARDINAL  POINTS.— North,  East,  South,  and  West.  (See 
Intercardinal  Points.) 

CELESTIAL. — Relating  to  the  heavens. 

CELESTIAL  CONCAVE.— The  heavens. 

CHART. — A  marine  map  showing  coasts,  shoals,  etc.,  etc. 


THE  NAVIGATOR'S  POCKET-BOOK  19 

All  charts  are  projected  true  (parallels  and  meridians  geographi- 
cal), but  the  compass  diagrams  printed  on  them  may  be  either 
true  or  magnetic,  as  described  under  the  head  of  Chart  Sailing. 
The  parallels  are  represented  by  straight  lines  drawn  true  east 
and  west  across  the  chart,  and  the  meridians  by  straight  lines 
drawn  true  north  and  south.  If  the  degrees  and  minutes  marked 
on  the  right  and  left  hand  margins  of  the  chart  increase  upward, 
the  chart  represents  north  latitudes,  but  if  they  decrease  upward 
the  chart  represents  south  latitudes.  If  the  degrees  and  minutes 
marked  on  the  top  and  bottom  margins  of  the  chart  increase 
toward  the  right  hand,  the  chart  represents  east  longitudes,  but 
if  they  decrease  toward  the  right  hand  the  chart  represents  west 
longitudes.  Charts  are  drawn  on  a  large  scale  or  a  small  scale 
according  to  the  extent  of  ocean  or  coast  to  be  delineated,  and  it 
is  to  be  understood  that  buoyage,  lights,  soundings,  etc.,  are 
fully  explained  on  the  charts  representing  the  waters  they  refer 
to,  and  such  explanations  and  directions  as  are  given  apply 
especially  to  that  particular  chart  on  which  the  details  are  read. 

Buoys  are  marked  B.  (black),  Cheq.  (chequered),  H.  S.  (hori- 
zontal stripes),  R.  (red),  W.  (white),  B.  W.  (black  and  white), 
B.  R.  (black  and  red),  R.  W.  (red  and  white),  V.  S.  (vertical 
stripes).  Buoys  painted  with  black  and  white  perpendicular 
stripes  mark  a  mid-channel  and  must  be  passed  close  to  to  avoid 
danger.  A  green  buoy  marks  a  wreck.  Perches  with  balls, 
cages,  etc.,  mark  turning-points  in  the  channel.  On  the  coast 
of  the  United  States,  when  approaching  a  channel  from  seaward, 
red  buoys  with  even  numbers  are  left  on  the  starboard  side,  and 
black  buoys  with  odd  numbers  are  left  on  the  port  side.  Buoys 
painted  with  red  and  black  horizontal  stripes  indicate  obstruc- 
tions with  channel-ways  on  either  side. 

The  quality  of  the  bottom  is  expressed  in  abbreviations,  as 


20  THE  NAVIGATOR'S  POCKET-BOOK 

follows:  blk.  (black),  b.  (blue),  bkn.  (broken),  br.  (brown),  cl. 
(clay),  co.  (coarse),  crl.  (coral),  d.  (dark),  f.  (fine),  gy.  (gray),  g. 
(gravel),  gn.  (green),  grd.  (ground),  h.  (hard),  m.  (mud),  oz. 
(ooze),  oys.  (oysters),  peb.  (pebbles),  rd.  (red),  r.  (rock),  rot. 
(rotten),  s.  (sand),  sh.  (shells),  sft.  (soft),  spk.  (speckled),  stf. 
(stiff),  st.  (stones),  wd.  (weed),  w.  (white),  y.  (yellow). 

Soundings,  unless  otherwise  specified,  are  indicated  according 
to  the  following  :  The  numerals  marked  on  the  white  surfaces 
represent  the  depth  of  the  water  at  that  point  in  fathoms  (six 
feet),  and  when  marked  on  the  dotted  surfaces  they  indicate  the 
depth  in  feet  (12  inches).  All  soundings  are  given  for  mean 
low  water,  and  the  rise  of  the  tide  at  the  given  place  is  to  be 
added  to  the  sounding  to  ascertain  the  greatest  depth  of  water 
at  high  tide  at  that  particular  point. 

During  fog  or  falling  snow,  vessels  approaching  light-ships 
will  be  warned  by  the  alternate  ringing  of  a  bell  and  the  blow- 
ing of  a  fog-horn. 

Lights  are  shown  by  a  dot  of  yellow  having  a  red  spot  in  the 
middle,  and  if  any  uncertainty  exists  concerning  the  character 
of  a  light  it  is  simply  marked  Lt.  Other  abbreviations  and 
their  significance  are  as  follows  :  F.  (fixed),  Fl.  (flashing),  Int. 
(intermittent),  Rev.  (revolving),  F.  and  Fl.  (fixed  and  flashing 
alternately),  Fig.  (floating),  Lt.  Ves.  (light- vessel).  When  no 
color  is  expressed  the  light  may  be  taken  to  be  white.  When- 
ever the  color  is  given  the  word  is  spelled  in  full,  as  red,  etc. 

Currents  are  shown  by  a  feathered  arrow;  the  direction  of  the 
same  indicating  the  flow  of  the  current.  Flood-tide  stream  is 
indicated  by  an  arrow  feathered  on  one  side  only,  and  ebb-tide 
stream  by  an  unfeathered  arrow. 

Rocks  just  below  the  surface  of  the  water  are  shown  by  a 
small  dotted  circle  having  a  cross  in  the  centre.  Rocks  awash 


THE  NAVIGATOR'S  POCKET-BOOK  21 

or  just  above  water  are  shown  by  a  dotted  circle  with  one  or 
more  dots  inclosed  according  to  the  number  or  extent  of  the 
rocks  indicated.  A  dotted  circle  with  a  numeral  in  it  signifies 
a  shoal  with  the  number  of  feet  or  fathoms  over  it.  Either  a 
rock,  an  island,  or  a  shoal  marked  E.  D.  signifies  existence 
doubtful,  and  if  marked  P.  D.,  it  means  position  doubtful,  al- 
though known  to  exist.  (See  Pricking  Position.) 

Mercator's  Chart. — This  is  the  chart  universally  adopted  as 
the  only  proper  chart  for  general  navigation.  The  parallels 
and  meridians  are  all  straight  parallel  lines,  but  the  meridians 
only  are  equidistant.  The  distance  between  the  parallels  in- 
creases from  the  equator  toward  the  poles  in  proportion  as  the 
meridians  converge.  This  chart  projection  is  constructed  by 
the  aid  of  the  table  of  meridional  parts  and  the  rule  given  in 
Bowditch. 

On  the  surface  of  the  globe  the  parallels  of  latitude  are  every- 
where equidistant,  while  the  distance  between  the  meridians 
lessens  as  we  proceed  polar  wise.  Thus  it  will  be  appreciated 
that  if  on  a  plane  chart  the  parallels  are  retained  equidistant 
while  the  meridians  are  widened  out  in  order  to  show  them  as 
straight  lines  and  as  far  apart  in  the  vicinity  of  the  poles  as 
they  are  at  the  equator,  there  must  be  considerable  distortion  in 
one  direction— namely,  the  longitude.  This  difficulty  of  de- 
lineation may  be  surmounted  and  the  relation  between  the 
principal  parts  maintained  by  also  distorting  the  chart  polarwise 
or  in  a  north  and  south  direction;  consequently  the  distance  be- 
tween the  parallels  is  widened  in  the  same  proportion  that  the 
meridians  have  been  widened.  Of  course  this  will  distort  the 
land  and  sea  more  and  more  in  the  parallels  approaching 
the  poles,  but  as  the  scale  on  the  right  and  left  hand  margins  of 
the  chart  allows  for  this,  and  as  the  contour  of  the  countries  is 


22  THE  NAVIGATOR'S  POCKET-BOOK 

preserved,  as  well  as  the  relative  directions  from  one  point  to 
another,  no  inconvenience  is  experienced  by  the  navigator. 
(See  Chart  Sailing.) 

Chart  of  the  Inclination. — A  chart  which  shows  the  dip  of 
the  magnetic  needle  for  various  latitudes  and  longitudes. 

Coast  Survey  Chart. — A  chart  of  the  coast  published  by 
Government. 

General  Chart. — A  chart  embracing  a  large  expanse  of  ocean 
or  extent  of  coast. 

Harbor  Chart. — A  chart,  as  its  name  implies,  which  de- 
lineates a  harbor. 

It  is  a  detached  portion  of  a  general  chart  and  is  shown  on  a 
large  scale.  As  a  rule  the  parallels  and  meridians  are  not 
shown  on  harbor  charts,  and  the  scale  is  given  in  miles. 

Physical  Chart. — A  chart  showing  ocean  currents,  winds, 
ice  limits,  etc. 

Great  Circle  Chart — A  chart  constructed  specially  so  that 
all  great  circles  are  represented  as  straight  lines.  This  answers 
the  same  purpose  for  great-circle  sailing  that  Mercator's  chart 
answers  for  rhumb-sailing.  The  construction  of  the  great-circle 
chart  is  such  that  a  straight  line  drawn  on  it  connecting  the 
place  of  departure  with  the  place  of  destination  gives  imme- 
diately the  great-circle  track. 

Hydrographic  Charts.— Charts  published  by  the  Washington 
Hydrographic  Office,  which  delineate  the  navigable  waters  of 
the  world,  rocks,  shoals,  tides,  currents,  depths,  etc.,  and  give 
the  varied  information  in  a  convenient  form  for  the  navigator. 
The  surveys  are  made  by  American  naval  officers  and  the  charts 
are  published  by  the  United  States  Government. 

Variation  Chart. — A  chart  of  the  world  on  Mercator's  pro- 
jection, on  which  is  represented  the  variation  of  the  compass  in 


THE  NAVIGATOR'S  POCKET-BOOK  23 

different  latitudes  and  longitudes  by  a  series  of  curved  lines ; 
also  known  as  an  isogonic  chart. 

CHART  SAILING. — This  ebmraces  several  considerations, 
which  will  be  taken  up  in  order. 

To  Shape  the  Course.— Place  the  same  bevelled  edge  of  the 
parallel  rules  over  the  ship's  place  and  the  point  bound  to  ;  then, 
preserving  the  angle,  slide  the  edge  to  the  nearest  compass  dia- 
gram printed  on  the  chart  until  it  lies  on  the  dot  in  the  centre  ; 
now  read  the  compass-point  looking  toward  the  place  sought, 
and  that  will  be  the  required  course.  (See  Course  Protractor ; 
Graduated  Rulers.) 

In  case  the  distance  between  the  two  places  is  too  great  to  be 
reached  by  the  parallel  rules,  take  a  piece  of  string  and  stretch 
it  from  one  point  to  the  other  by  the  aid  of  pins  stuck  in  the 
chart  through  the  two  places  ;  then  lay  the  bevelled  edge  of  the 
rule  against  the  string  to  obtain  the  angle,  and  proceed  as  before 
explained. 

To  Allow  for  Variation. — On  some  charts  the  north  and 
south  line  of  the  diagram  compass  is  parallel  with  the  meridian 
line,  while  on  other  charts  the  north  and  south  line  of  the  dia- 
gram compass  forms  an  angle  with  the  meridian  line.  In  the 
latter  case  it  proves  that  the  diagram  indicates  magnetic  direc- 
tions ;  consequently  the  course  found  by  the  parallel  rules  will 
be  steered  (unless  deviation  exists),  as  the  diagram  on  the  chart 
is  a  reflection  of  the  compass  on  board  the  vessel.  On  the  other 
hand,  where  the  north  and  south  line  of  the  diagram  compass 
is  parallel  with  the  meridian,  it  proves  that  the  diagram  indi- 
cates true  or  geographical  directions.  In  this  case  it  becomes 
necessary  to  allow  for  the  variation  of  the  compass  as  fol- 
lows : 

Example. — Suppose  that  the  course  found  by  a  true  compass 


24  THE  NAVIGATOK'S  POCKET-BOOK 

diagram  is  north  and  the  chart  tells  us  that  where  the  ship  is 
situated  there  is  one  point  of  westerly  variation,  which  means 
that  the  north  end  of  the  compass  needle  is  inclined  one  point 
to  the  west  of  the  true  or  geographical  north.  Under  these 
circumstances,  it  will  be  necessary  to  steer  north-by-east  by  the 
ship's  compass  in  order  to  make  a  true  north  course. 

Note. — A  simple  rule  to  remember  for  converting  true  courses 
into  magnetic  courses  is  to  allow  the  amount  of  westerly  varia- 
tion away  from  the  true  course  in  the  direction  that  the  hands 
of  a  watch  revolve,  and  easterly  variation  contrary,  or  against 
the  hands  of  a  watch. 

To  Allow  for  Deviation. — If  deviation  exists  for  the  correct 
magnetic  course  found,  then  the  correct  magnetic  course  must 
have  the  amount  of  the  deviation  applied  to  it  on  exactly  the 
same  principle  as  explained  for  variation  in  the  preceding  para- 
graph. 

Example. — The  correct  magnetic  course  is  east  and  there  is 
one  point  of  westerly  deviation  to  be  allowed  when  the  ship's 
head  is  on  that  course  ;  consequently  the  compass  course  to  be 
steered  is  east-by-south  in  order  to  make  a  correct  magnetic  east 
course. 

Always  apply  the  variation  before  applying  the  deviation. 

To  Measure  the  Distance. — On  a  large  scale  chart,  as  for 
example,  Long  Island  Sound,  take  off  five  miles  or  more  be- 
tween the  points  of  the  dividers,  measuring  from  the  latitude 
scale  on  the  side  of  the  chart,  then  see  how  many  times  this 
span  is  contained  on  the  line  of  the  course. 

On  a  chart  of  small  scale,  such  as  an  ocean  chart,  find  the 
middle  latitude  between  the  two  places,  then  take  off  one  or 
more  degrees  from  this  middle  point,  which  will  give  the 
average  length  of  a  degree  in  those  latitudes.  If  sailing  on  a 


THE  NAVIGATOR'S  POCKET-BOOK  25 

parallel  (an  east  or  west  course)  set  the  dividers  to  the  scale 
opposite  the  parallel. 

The  reason  for  setting  the  dividers  to  the  scale  opposite  the 
parallels  to  be  sailed  in  is  on  account  of  that  particular  scale 
belonging  to  those  parallels.  As  explained  under  the  head  of 
Charts,  the  distance  between  the  parallels  increases  from  the 
equator  toward  the  poles,  consequently  the  scale  given  for  the 
parallels  near  the  equator  will  not  answer  for  higher  latitudes. 

The  two  graduated  parallels  (top  and  bottom  margins  on  bor- 
ders) on  the  chart  are  marked  in  degrees  and  minutes,  but  on 
these  parallels  longitude-in-arc  is  measured,  nothing  more  ;  dis- 
tance cannot  be  taken  from  them,  and  they  are  only  employed 
for  laying  off  the  longitude. 

Cross-Bearings — Observe  in  quick  succession  the  compass- 
bearings  of  two  lights  (or  other  stationary  objects  which  are 
denned  on  the  chart),  then  refer  to  the  chart,  and  by  the  aid  of 
the  parallel  rules  and  the  magnetic  diagram  compass  draw  pencil 
lines  along  the  paper  from  the  lights  in  question,  according  to 
the  respective  bearings  of  the  two  objects,  and  the  point  where 
the  lines  cross  will  show  the  position  of  the  ship  at  the  time  the 
bearings  were  taken. 

Remarks. — It  is  to  be  understood  that  the  compass  bearings 
are  to  be  corrected  for  the  deviation  (if  any  exists)  of  the  ship's 
head  at  the  time  the  bearings  were  taken,  so  as  to  convert  them 
into  correct  magnetic  bearings  before  applying  the  lines  to  the 
chart. 

It  must  be  remembered  that  if  the  chart  is  provided  with  true, 
instead  of  magnetic  compass  diagrams,  the  variation  of  the  com- 
pass must  also  be  applied  to  the  respective  bearings  in  order  to 
convert  them  into  true  bearings  ;  then  these  latter  must  be  trans- 
ferred to  the  chart,  plotting  them  from  the  true  compass  diagram. 


26  THE  NAVIGATOR'S  POCKET-BOOK 

Vertical  Danger  Angle. — The  danger  angle  has,  to  a  great 
extent,  taken  the  place  of  cross-bearings  for  locating  the  posi- 
tion of  a  vessel  when  in  sight  of  lighthouses,  either  by  day  or 
night.  It  is  extremely  easy  of  solution,  and  by  the  aid  of  the 
danger-angle  tables  to  be  found  in  the  back  of  this  little  volume 
the  navigator  will  discover  it  to  be  a  very  simple  matter,  both  to 
fix  the  position  of  his  ship  and  to  keep  outside  of  dangers  in  the 
way  of  rocks  and  shoals  situated  at  a  distance  from  the  shore. 
(See  Danger- Angle  Tables.) 

First  Consideration. — To  determine  the  place  of  the  ship, 
take  a  compass-bearing  of  any  lighthouse  in  sight ;  the  vessel 
will  be  somewhere  on  this  line  of  bearing.  Then  with  the 
sextant  measure  the  altitude  of  the  light  by  throwing  the  reflec- 
tion of  the  lantern  to  the  water  line.  By  consulting  the  danger- 
angle  tables  with  the  measured  angle  and  the  height  of  the  light 
above  the  sea-level  (the  latter  is  given  on  the  chart)  the  distance 
of  the  vessel  seawards  from  the  light  will  be  read  in  the  side 
column  to  the  left. 

Second  Consideration. — To  explain  another  practical  applica- 
tion of  the  vertical  danger  angle,  let  it  be  supposed  that  a  ves- 
sel is  forced  to  closely  round  a  lighthouse,  at  some  distance 
seawards  of  which  there  is  a  cluster  of  rocks  a  few  feet  under 
water.  Now  with  the  dividers  measure  the  distance  from  the 
light  to  a  point  well  outside  of  the  danger,  then  with  this  dis- 
tance and  the  height  of  the  light  enter  the  danger-angle  tables 
and  read  the  angle  given.  Place  this  angle  on  the  sextant  and 
when  approaching  and  passing  the  light  observe  that  this  angle 
does  not  increase,  otherwise  the  ship  will  be  inside  the  danger 
mark.  If  the  angle  decreases  the  ship  will  be  farther  outside 
the  danger  mark  than  there  is  necessity  for. 

Remarks. — In  measuring  vertical  danger  angles,  when  the 


THE  NAVIGATOR'S  POCKET-BOOK  27 

lighthouse  is  comparatively  close,  the  observer  should  get  as 
near  to  the  surface  of  the  water  as  the  deck  will  admit  in  order 
to  reduce  the  error  arising  from  the  eye  being  elevated  above 
the  sea  •  level.  It  is  to  be  explained,  however,  that  if  this 
point  is  disregarded  altogether,  the  slight  error  will  lie  on  the 
safe  side,  so  long  as  there  exists  no  danger  seawards  of  the 
ship. 

If  the  sextant  has  an  index-error  the  same  must  be  allowed 
for  in  measuring  danger  angles.  (See  Sextant.) 

Horizontal  Danger  Angle. — Where  the  vertical  danger  angle 
is  dependent  upon  a  lighthouse,  the  height  of  which  is  known, 
the  horizontal  danger  angle  may  not  only  be  worked  by  two 
lighthouses  independent  of  their  height,  but  in  the  daytime  it 
may  be  employed  by  using  any  two  well-defined  objects  on 
shore,  such,  for  instance,  as  prominent  features  of  the  coast-line, 
buildings,  etc.  In  the  horizontal  danger  angle  no  tables  are 
used,  the  navigator  calculating  his  own  angle. 

We  will  suppose  that  the  chart  shows  a  number  of  rocks  or 
shoals  stretching  for  some  little  distance  along  the  coast,  and 
that  back  of  them  on  the  shore  are  a  life-saving  station  and  a 
church.  Sweep  the  smallest  circle  with  a  pencil  point  dividers 
that  will  pass  through  the  two  shore  objects  and  inclose  all  the 
dangerous  features  between  them.  Now  from  a  seawards  point 
on  this  circle,  draw  lines  to  the  two  objects  on  shore  so  that  the 
lines  will  look  like  the  plotting  of  a  cross-bearing.  The  respect- 
ive directions  of  these  two  lines  will  be  measured  by  the  parallel 
rules  and  the  nearest  chart  compass,  and  the  angle  shown  by  the 
divergence  of  the  lines  will  be  turned  into  degrees.  This  angle 
will  be  placed  on  the  sextant,  and  when  approaching  and  pass- 
ing the  danger  the  navigator  will  observe  that  the  angle  does 
not  increase,  otherwise  he  will  know  that  he  is  inside  the  danger 


28  THE  NAVIGATOR'S  POCKET-BOOK 

line.  If  the  angle  decreases  it  is  a  sign  that  he  is  outside  or  sea- 
wards of  the  danger  line. 

As  its  name  implies,  this  angle  is  measured  by  holding  the 
sextant  horizontal  and  sweeping  one  object  into  the  other. 

It  matters  not  from  what  seawards  point  of  the  circumference 
of  this  circle  the  angle  is  measured — it  will  give  the  same  re- 
sult ;  consequently  by  steering  the  ship  so  as  to  preserve  the 
given  angle,  the  navigator  would  sail  right  around  the  circle 
drawn  by  the  pencil-point  dividers. 

Example. — We  will  suppose  that  off  a  section  of  the  coast 
defined  by  two  headlands,  several  clusters  of  rock  are  shown  to 
extend  between  them  and  to  lie  off  shore  at  a  distance  of  two 
miles.  Our  course  being  close  along  the  coast  it  is  necessary  to 
take  precautions  in  approaching  and  passing  this  dangerous 
point. 

By  the  aid  of  a  pencil-point  dividers  (or  a  small  piece  of  lead- 
pencil  fastened  to  one  leg  of  the  common  dividers)  we  sweep  a 
circle  which  passes  through  the  headlands  and  incloses  every 
part  of  the  shoal.  Next  we  draw  two  pencil  lines  from  a  sea- 
wards point  on  this  circle  so  that  they  will  pass  through  each 
headland  ;  then  we  ^determine  their  respective  bearings  by  the 
parallel  rules  and  the  chart  compass. 

One  headland,  we  will  say,  we  find  to  bear  north-northeast, 
and  the  other  northwest.  These  bearings  equal  six  compass- 
points,  or  67°;  consequently  this  is  the  horizontal  danger  angle, 
and  we  place  the  same  on  the  sextant  and  observe  that  it  does 
not  increase  as  we  approach  and  pass  the  shoal. 

Four-Point  Bearing. — This  is  an  extremely  simple  and  use- 
ful problem.  "When  approaching  a  lighthouse,  light-vessel,  or 
a  point  of  land,  note  its  compass-bearing  when  it  is  four  points 
on  the  bow.  When  the  object  is  exactly  abeam  calculate  the 


THE  NAVIGATOR'S  POCKET-BOOK  29 

distance  run  from  the  time  the  first  bearing  was  taken,  and  this 
will  be  the  distance  of  the  ship  from  the  light  abeam. 

Example. — A  ship  is  steering  north,  making  ten  knots  per 
hour.  At  7  o'clock  a  lighthouse  bears  northwest,  and  at  7.30 
o'clock  it  bears  west,  or  directly  abeam.  The  distance  run  in 
the  interval  is  five  miles  ;  consequently  the  ship  is  five  miles  east 
of  the  light. 

Remarks. — The  ship  is  not  supposed  to  change  her  course  in 
the  interval  between  bearings. 

In  this  problem  the  deviation  of  the  compass  is  not  considered, 
as  the  vessel  maintains  the  same  course  ;  consequently,  the  devia- 
tion being  the  same  for  both  bearings,  it  is  ignored. 

An  object  to  bear  directly  abeam  must  subtend  an  angle  of 
eight  points  of  the  compass,  or  90°,  to  the  ship's  course  ;  for  ex- 
ample, if  a  ship  is  steering  northwest,  an  object  will  be  directly 
abeam  on  the  port  side  when  it  bears  southwest,  and  directly 
abeam  on  the  starboard  side  when  it  bears  northeast. 

Patterson's  Method. — This  conception  of  the  author's  affords 
the  means  of  locating  the  vessel  by  two  compass-bearings  of  the 
same  object  when  in  sight  of  land,  where  only  a  single  light, 
headland,  or  other  fixed  feature  is  to  be  seen. 

Rule.— Observe  the  bearing  of  the  object  and  note  the  time. 
After  holding  the  course  until  the  object  has  changed  its  bearing 
at  least  two  or  three  points,  note  again  its  bearing  and  the  time, 
and  calculate  the  distance  the  vessel  has  run  in  the  interval  be- 
tween the  first  and  last  bearings.  Trace  the  two  lines  of  bear- 
ing on  the  chart  in  pencil,  then  span  the  dividers  to  the  distance 
run,  and  proceed  as  follows : 

With  the  parallel  rules  set  to  the  course  sailed  by  the  ship  'be- 
tween bearings,  move  them  along  the  pencil  lines  until  both 
points  of  the  dividers,  held  against  the  bevelled  edge  of  the  rules, 


30  THE  NAVIGATOR'S  POCKET-BOOK 

just  fit  across  the  lines,  and  these  two  points  where  the  dividers 
rest  will  show  the  position  of  the  vessel  at  the  time  of  the  first 
bearing  as  well  as  her  place  at  the  time  of  the  second  bearing. 

Remarks. — The  two  compass-bearings  must  be  corrected  for 
the  deviation  (if  any  exists)  of  the  ship's  head  at  the  time  the 
bearings  were  taken,  so  as  to  convert  them  into  correct  magnetic 
bearings  before  tracing  them  on  the  chart. 

The  compass  course  must  also  have  the  deviation  applied  to 
it  so  as  to  reduce  it  to  a  correct  magnetic  course  before  setting 
the  parallel  rules  by  the  diagram  compass  on  the  chart. 

CHIP  LOG. — This  log  can  claim  at  least  one  advantage  over 
the  patent  log,  inasmuch  as  the  vessel's  rate  of  speed  can  be  de- 
termined by  it  at  any  given  instant,  whereas  the  patent  log  is 
useful  only  for  recording  a  considerable  distance  run. 

The  log  line  should  be  about  one  hundred  and  fifty  fathoms 
long  and  marked  off  in  knots,  the  distance  between  which  should 
stand  for  the  same  part  of  a  sea  mile  as  the  30  seconds  sand- 
glass stands  for  an  hour — namely,  the  120th  part — which  would 
make  the  lengths  between  the  knots  about  fifty-one  feet.  When 
a  28  seconds  glass  is  used  the  length  between  the  knots  should 
be  about  forty-seven  feet. 

It  has  been  found,  however,  from  practical  experience,  that 
the  chip  log  records  somewhat  less  than  it  should  owing  to  the 
log  coming  home  after  being  hove.  To  compensate  for  this, 
navigators  should  shorten  the  distance  between  the  knots  so  that 
for  a  30  seconds  glass  they  should  be  forty-eight  feet  apart,  and 
for  a  28  seconds  glass,  forty -five  feet  apart. 

Heaving  the  Log. — One  man  holds  the  reel  and  another  the 
sand-glass.  The  officer  throws  the  log  chip  over  the  ship's  stern, 
and  when  he  observes  that  the  stray  line  is  run  off  (about  ten  fath- 
oms—this distance  being  allowed  to  carry  the  log  out  of  the  in 


THE  NAVIGATOR'S  POCKET-BOOK  31 

fluence  of  the  ship's  wake),  he  calls  "  turn  ; "  the  seaman  upsets 
the  glass  and  watches  until  the  sand  is  run  out,  then  calls  "  stop." 
The  officer  stops  the  line  by  a  sudden  jerk  which  pulls  the  plug 
out  of  its  hole  in  the  chip  and  so  allows  the  log  to  float  horizon- 
tal, then  observes  the  number  of  marks  that  have  passed  over  the 
taffrail.  The  last  mark  shown  indicates  the  knots,  and  the  dis- 
tance of  the  mark  outside  of  the  taif rail  shows  the  fractions  of 
the  knot  estimated  in  eighths  (eight  furlongs  to  the  mile).  The 
knots  and  furlongs  give  the  speed  of  the  vessel  in  nautical  miles 
or  knots. 

Remarks. — When  running  before  a  heavy  sea,  allowance 
must  be  made,  for  the  ship  will  make  greater  speed  than  indi- 
cated by  the  log.  Under  such  conditions  it  is  customary  to  add 
one  mile  for  every  ten  knots  run  out. 

Driving  against  a  heavy  sea  it  is  the  rule  to  subtract  one  mile 
for  every  ten  knots  run  out. 

In  heaving  the  log,  the  line  must  be  helped  from  the  reel  by 
the  officer,  so  that  no  strain  is  brought  upon  the  chip  as  it  rests 
in  a  perpendicular  position  in  the  water  ;  otherwise  the  wooden 
peg  which  forms  a  part  of  the  bridle  will  pull  out  and  the  log 
will  lie  flat  on  the  surface. 

The  line  must  be  measured  occasionally,  and  if  it  is  found  to 
be  stretched,  it  must  be  carefully  remarked,  otherwise  it  will 
prove  deceptive. 

Compare  the  sand-glass  at  times  with  a  watch  to  see  that  it  runs 
out  in  the  prescribed  number  of  seconds. 

The  glass  is  more  or  less  influenced  by  the  weather,  running 
slower  in  a  damp  atmosphere  than  in  a  dry  one. 

In  case  of  accident  to  the  sand-glass,  time  the  log-line  by  a 
watch. 

When  a  vessel  is  going  at  a  high  rate  of  speed  it  is  usual  to  use 


32  THE  NAVIGATOR'S  POCKET-BOOK 

a  14  seconds  glass  and  then  double  the  indicated  number  of  knots  • 
this  saves  the  paying  out  of  a  long  length  of  line  and  the  at- 
tendant effort  of  hauling  it  in. 

The  first  knot  on  the  log  line  is  measured  from  the  white  rag, 
which  terminates  the  ten  fathoms  allowed  to  drift  the  chip  far 
enough  astern  to  be  out  of  the  eddies  of  the  wake.  When  this 
white  rag  passes  over  the  taffrail  the  sand-glass  is  turned. 

CHRONOMETER. — A  marine  time-piece  constructed  with 
the  idea  of  great  accuracy,  and  set  to  the  time  of  some  first  me- 
ridian. The  Americans  and  English  use  the  time  of  the  me- 
ridian of  Greenwich  ;  the  French  that  of  Paris,  etc. 

Care  of  Chronometers. — Chronometers  should  be  wound  at 
the  same  hour  each  day,  the  key  being  turned  gently  so  that  no 
shock  may  be  imparted  when  the  key  butts.  They  should  be 
stowed  as  near  the  centre  of  motion  as  possible,  and  the  tempera- 
ture near  them  kept  as  uniform  as  possible.  When  transported 
by  hand  they  should  be  clamped  securely  by  the  clamp-screw, 
to  prevent  them  from  swinging  about  in  their  gimbals.  In  wind- 
ing a  chronometer  the  instrument  is  to  be  inverted  with  the  left 
hand  and  the  key  turned  with  the  right.  At  all  times,  except 
when  being  transported  by  hand,  the  chronometer  must  be  left 
to  swing  freely  in  its  gimbals,  like  a  compass.  Never  stow  a 
chronometer  close  against  an  iron  bulkhead,  or  near  an  iron 
stanchion,  or,  beyond  all,  near  spare  compasses  or  artificial 
magnets,  otherwise  magnetism  will  be  induced  into  the  steel 
balance  and  ruin  the  going  of  the  chronometer.  Avoid  placing 
a  chronometer  in  the  after-end  of  a  screw  steamer  on  account  of 
the  vibration .  When  a  chronometer  is  being  transported  by  hand 
be  careful  not  to  knock  it  against  anything  or  to  give  it  a  sud- 
den twist.  (See  Rate.) 


THE  NAVIGATOR'S  POCKET-BOOK  33 

CHRONOMETER  COMPARISON.  —  To  determine  the 
error  of  a  chronometer  by  observatory  clocks  or  by  comparing 
the  longitude  of  the  ship  found  by  observation  with  the  known 
longitude  of  a  visible  point  of  land. 

CHRONOMETER  RATE.— (See  Rate.) 

CHRONOMETER-TIME  SIGHT.— (See  Longitude.) 

CIRCUM-MERIDIAN  ALTITUDE — An  altitude  of  a 
heavenly  body  observed  a  short  time  before  or  after  its  meridian 
passage.  This  is  also  known  as  an  ex-meridian  altitude.  (See 
Latitude.) 

CIRCUMNAVIGATE.— To  sail  completely  around.  To 
sail  around  the  world  is  to  circumnavigate  it. 

CIRCUMNAVIGATOR'S  DAY.  —  In  circumnavigating 
the  globe  by  sailing  west  the  ship  and  the  sun  move  in  the  same 
direction,  but  by  sailing  east  the  ship  and  the  sun  move  in  oppo- 
site directions.  In  the  former  case  the  sun  overtakes  the  ship, 
and  in  the  latter  case  the  sun  advances  to  meet  the  ship.  There- 
fore in  sailing  west  the  ship's  day  is  lengthened  and  in  sailing 
east  it  is  shortened  at  t^e  rate  of  one  hour  for  every  15°  of 
longitude  made. 

Should  a  vessel  start  from  Greenwich  and  sail  east  until  the 
meridian  of  180°  was  reached,  arriving  at  that  point  at  2  o'clock 
in  the  morning  of  Sunday,  the  20th  day  of  the  month  (according 
to  the  ship's  date  and  time),  it  would  only  be  2  o'clock  in 
the  afternoon  at  Greenwich  on  Saturday,  the  19th.  Thus  the 
ship's  time  would  be  twelve  hours  ahead  of  the  time  at  Green- 
wich. Now  if  the  ship,  without  changing  her  date,  continued 
sailing  to  the  eastward  until  Greenwich  was  reached,  another 
twelve  hours  would  be  gained,  and  the  ship's  time  would  be 
twenty-four  hours,  or  one  day,  ahead  of  the  Greenwich  time. 
3 


34  THE  NAVIGATOR'S  POCKET-BOOK 

On  the  other  hand,  should  a  vessel  start  from  Greenwich  and 
sail  west  until  the  meridian  of  180°  was  reached,  arriving  at  that 
point  at  2  o'clock  in  the  morning  of  Sunday,  the  20th  day  of 
the  month  (according  to  the  ship's  date  and  time),  it  would  be 
2  o'clock  in  the  afternoon  of  the  same  day  (Sunday,  20th)  at 
Greenwich,  so  that  the  ship's  time  would  be  twelve  hours  behind 
the  Greenwich  time.  If  the  ship,  without  changing  her  date, 
continued  to  sail  to  the  westward  until  Greenwich  was  reached, 
another  twelve  hours  would  be  lost,  and  the  ship's  time  would 
be  twenty- four  hours,  or  one  day,  behind  the  Greenwich  time. 

Rule. — When  crossing  the  meridian  of  180°,  if  the  ship  is 
sailing  eastward,  the  navigator  must  reckon  the  given  day  over 
again,  so  that  there  will  be  two  Sundays,  or  Mondays,  or  Tues- 
days, etc. ,  in  the  log-book  for  that  particular  week,  according  to 
the  day  that  he  crosses.  By  doing  this  the  ship's  date  will  be 
found  to  correspond  with  the  Greenwich  date  when  the  vessel 
reaches  that  port. 

But  when  crossing  the  meridian  of  180°,  if  the  ship  is  sailing 
westward,  the  navigator  must  skip  a  day,  so  that  there  will  be  a 
Sunday,  or  a  Monday,  or  a  Tuesday,  etc.,  omitted  in  the  log- 
book for  that  particular  week,  according  to  the  day  that  he 
crosses.  This  insures  the  ship's  date  agreeing  with  the  Green- 
wich date  when  the  vessel  reaches  the  latter  port. 

Warning. — The  great  point  for  the  navigator  to  bear  in  mind 
is  that  he  is  not  to  interfere  with  the  Greenwich  date  shown  by 
the  chronometer,  but  that  he  is  religiously  to  keep  the  run  of 
and  hold  on  to  same,  and  select  the  sun's  declination,  equation, 
etc.,  from  the  nautical  almanac  for  the  Greenwich  date,  and  cor- 
rect the  hourly  difference  of  declination,  etc.,  according  to  the 
regular  rule  given  under  the  head  of  Declination. 

Examples. — A  ship  leaves  Greenwich  and  sails  east,  reaching 


THE  NAVIGATOR'S  POCKET-BOOK  35 

the  meridian  of  180°  on  Sunday,  the  20th  (according  to  the 
ship's  date).  Instead  of  calling  the  next  day  Monday,  the  21st, 
it  must  be  considered  again  as  Sunday,  the  20th,  so  that  two  Sun- 
days and  two  20th  days  for  that  month  will  appear  in  succession 
in  the  log-book. 

A  ship  leaves  Greenwich  and  sails  west,  reaching  the  meridian 
of  180°  on  Sunday,  the  20th  (according  to  the  ship's  date).  In- 
stead of  calling  the  next  day  Monday,  the  21st,  it  must  be  con- 
sidered as  Tuesday,  the  22d,  so  that  there  will  not  appear  either 
a  Monday  or  a  21st  day  for  that  month  in  the  log  book. 

CIVIL  TIME. — The  civil  day  consists  of  twenty-four  hours  ; 
it  commences  at  midnight,  and  the  first  twelve  hours  are  called 
A.M.,  and  the  latter  twelve  hours  are  called  P.M.  (See  A.M.  P.M.) 

CLAMP-SCREW.— (See  Sextant.) 
CLOUDS.— (See  Weather.) 

COLLIMATION.— The  line  of  sight  in  the  direction  of  any 
object.  (See  Axis  of  Collimation.) 

COMBINED  ALTITUDE  PROBLEM.— (See  Sumner's 
Method.) 

COMPASS.— The  mariner's  compass  consists  of  a  magnetized 
steel  bar  secured  parallel  to  the  north  and  south  line  of  a  circu- 
lar card,  which  latter  is  balanced  on  a  pivot  so  as  to  turn  freely 
in  the  horizontal  plane  and  to  indicate  the  magnetic  meridian. 
The  surface  of  the  card  is  divided  into  thirty-two  courses  with 
their  intermediate  quarters,  and  in  addition  to  this  all  steam- 
ships have  the  circumference  of  the  compass  card  graduated  into 
degrees. 

Boxing  the  Compass. — What  is  known  as  boxing  the  com- 
pass is  calling  the  thirty-two  courses  in  order  from  north  by  the 


36  THE  NAVIGATOR'S  POCKET-BOOK 

way  of  east,  as  shown  on  the  diagram  in  front  of  this  book. 
To  box  the  compass  backward  is  to  call  the  courses  from  north 
by  the  way  of  west,  or  contrary  to  the  order  in  which  the  hands 
of  a  watch  revolve. 

Points  and  Degrees. — By  consulting  the  diagram  it  will  be 
seen  that  compass  courses  are  given  a  value  both  in  points  and 
degrees,  the  same  commencing  at  the  two  poles  of  the  circle 
(north  and  south)  and  ending  at  the  equator  line  of  the  compass 
(east  and  west).  Thus  the  north  and  south  points  are  zero  and 
the  east  and  west  points  have  a  numerical  value  of  8  and  an 
angular  value  of  90°. 

Variation  of  the  Compass.— The  compass  needle  when  un- 
influenced by  deviation  points  to  the  magnetic  poles  of  the  earth, 
and  as  these  do  not  coincide  with  the  true  or  geographical  poles, 
the  magnetic  meridians  form  an  angle  with  the  true  meridians, 
and  this  is  called  the  variation  of  the  compass,  which  varies  in 
extent  in  different  parts  of  the  world.  The  magnetic  north  pole 
is  situated  on  the  parallel  of  70°  north  and  the  meridian  of  97e 
west.  The  magnetic  south  pole  is  situated  on  the  parallel  of  73° 
south  and  the  meridian  of  146°  east. 

Over  the  North  Atlantic,  the  greater  part  of  the  South  At- 
lantic, and  the  Indian  Ocean,  the  variation  is  westerly,  and  over 
a  part  of  the  South  Atlantic  and  in  the  Pacific  the  variation  is 
easterly.  There  are  places  on  the  surface  of  the  globe  where 
variation  does  not  exist,  or  in  other  words,  where  the  compass 
points  true  north,  and  these  places  are  said  to  be  situated  on  the 
line  of  no  variation.  One  of  these  lines  runs  through  Eastern 
Europe,  Asia,  and  Australia  ;  the  other  through  North  Ameri- 
ca, the  eastern  part  of  South  America,  and  the  southwestern 
part  of  the  South  Atlantic  Ocean. 

The  magnetic  equator  is  not  the  same  as  the  earth's  equator, 


THE  NAVIGATOR'S  POCKET-BOOK  37 

but  an  irregular  line  running  round  the  globe,  near  the  earth's 
equator,  which  it  crosses  in  two  places,  one  near  the  west  coast 
of  Africa,  the  other  about  the  middle  of  the  Pacific  Ocean. 

The  variation  of  the  compass  is  not  constant,  but  undergoes 
an  annual  change,  and  the  amount  of  this  yearly  increase  or  de- 
crease will  be  found  plainly  marked  on  charts. 

Deviation  of  the  Compass.— What  is  known  as  the  devia- 
tion of  the  compass  is  the  deflection  of  the  needle  from  the 
magnetic  meridian,  caused  in  iron  sailing  ships  by  the  attraction 
of  the  hull  and  iron  lowermasts,  and  in  an  iron  steamship  by 
the  attraction  of  the  hull,  machinery,  smokestack  and  masts. 
In  addition  to  this  it  must  be  understood  that  deviation  is  often 
caused  by  certain  elements  of  magnetism  in  the  cargo.  The 
manner  of  ascertaining  the  existence  and  extent  of  compass  de- 
viation will  be  found  explained  under  the  heads  of  Amplitude 
and  Azimuth.  When  shaping  a  course,  or  when  taking  com- 
pass-bearings, the  deviation  existing  for  the  ship's  head  must  be 
considered,  as  explained  under  the  head  of  Chart  Sailing.  De- 
viation is  named  east  or  west  according  as  the  north  point  of 
the  compass  is  drawn  to  the  eastward  or  westward  of  the  mag- 
netic meridian. 

Deviation  Card.— This  is  a  tabulated  account  of  the  devia- 
tion of  the  compass  for  each  one  of  the  thirty-two  courses,  and 
directs  the  navigator  as  to  the  course  to  be  steered  by  compass 
in  order  to  make  the  required  correct  magnetic  course.  Devia- 
tion always  refers  to  the  ship's  head.  In  other  words,  where 
deviation  is  given  it  means  for  a  certain  course.  If  the  card 
tells  us  that  for  an  east  course  the  compass  has  10°  of  westerly 
deviation,  it  signifies  that  when  the  ship  heads  east  the  north  end 
of  the  compass  needle  will  be  drawn  10°  to  the  westward  of  the 
correct  magnetic  north,  and  any  bearing  taken  when  the  ship  is 


38  THE   NAVIGATOR^  POCKET-BOOK 

on  such  course  must  be  corrected  for  10°  of  westerly  deviation, 
and  not  for  the  deviation  given  for  the  point  represented  by  the 
bearing. 

A  deviation  card  refers  to  one  particular  compass,  and  to  no 
other,  consequently  a  course  set  or  a  bearing  taken  by  a  certain 
compass  must  have  the  deviation  of  that  compass  applied  to  it 
according  to  its  own  deviation  card. 

Residual  Errors. — When  a  compass  is  affected  by  deviation 
it  is  sought  to  adjust  it  by  placing  artificial  magnets  in  its 
vicinity,  so  as  to  draw  the  compass  needle  to  the  correct  mag- 
netic meridian,  and  the  remaining  deviations  for  the  various 
courses  are  classed  as  residual  errors. 

Local  Attraction  of  the  Compass. — Elements  of  magnetism 
outside  (away)  from  the  vessel  which  influence  the  pointing  of 
the  compass.  In  sailing  very  close  along  some  coasts  where 
there  are  large  deposits  of  iron  ore  or  volcanic  disturbances  the 
compass  has  been  found  to  be  slightly  and  temporarily  drawn 
away  from  the  correct  magnetic  north.  It  will  be  understood 
that,  as  its  name  implies,  this  disturbing  quantity  is  purely 
local.  A  vessel's  compass  is  often  affected  when  lying  alongside 
of  a  dock  or  other  vessel,  owing  to  the  near  presence  of  iron 
used  in  construction  of  same.  (See  Compensated,  Demagnet- 
ized, Dry,  Elevated,  Liquid,  Masthead,  Oil,  Pole,  Spirit,  Stand- 
ard, Steering,  and  Tripod  Compasses.) 

COMPASS  ADJUSTING.— Correcting  a  compass  for  devia- 
tion by  placing  artificial  magnets  in  its  immediate  vicinity,  so  as 
to  draw  the  north  end  of  the  compass  needle  to  the  correct  mag- 
netic north.  As  a  rule  compass  adjusting  is  performed  by  pro- 
fessional adjusters,  it  being  a  profession  in  itself,  although  there 
are  shipmasters  who  have  made  a  study  of  the  science,  and  in 
consequence  are  able  to  dispense  with  outside  talent.  In  the 


THE  NAVIGATOR'S  POCKET-BOOK  39 

fase  of  the  patent-adjusting-binnacle  compass,  where  the  mag- 
nets are  contained  in  racks  within  the  binnacle  stand,  full  direc- 
tions for  adjusting  the  compass  are  furnished  with  the  instru- 
ment. 

COMPASS-BEARING. — The  direction  of  an  object  accord- 
ing to  one  of  the  divisions  of  the  compass  card. 

COMPASS  CARD.— The  circle  to  which  is  secured  the  mag 
netized  bar  of  steel  and  on  which  circle  the  thirty-two  compass 
courses  are  shown. 

COMPASS  CORRECTIONS. --Allowances  for  variation 
and  deviation. 

COMPASS  COURSE.— The  track  made  by  a  vessel  accord- 
ing to  one  of  the  divisions  of  the  compass  card. 

COMPASS  NEEDLE.— The  name  often  applied  to  the 
magnetized  steel  bar  secured  to  the  compass  card. 

COMPASS  POINT.— One  of  the  divisions  of  the  compass 
card. 

COMPASS  ROSE. —  The  diagram  compass  on  a  chart  is 
referred  to  in  some  works  on  navigation  as  a  compass  rose. 

COMPENSATED  COMPASS.— An  adjusted  compass ;  a 
compass  that  has  been  freed,  to  a  greater  or  less  extent,  of  its 
deviation  by  the  employment  of  artificial  magnets,  the  same 
being  placed  in  close  proximity  to  the  compass,  so  as  to  draw 
the  needle  to  the  correct  magnetic  meridian. 

COMPENSATING  MAGNETS.— Artificial  magnets  used 
in  compass  adjusting.  (See  Magnet.) 

COMPLEMENT.— The  full  number  or  quantity;  what  an 
altitude  lacks  of  90° .  The  zenith  distance  is  the  complement 
of  the  altitude. 


iO  THE  KAVIGATOR'S  POCKET-BOOK 

OO-LATITUDE.— The  complement  of  the  latitude,  or  what 
it  lacks  of  90°;  as,  for  instance,  50°  is  the  co-latitude  of  40°. 

COMPOSITE  SAILING. — This  is  a  combination  of  great- 
circle  and  parallel  sailing,  and  is  adopted  when  the  great-circle 
track,  by  passing  in  the  neighborhood  of  ice,  land,  or  other  dan- 
ger, becomes  impracticable.  In  other  words,  it  is  a  modification 
of  the  great-circle  track.  (See  Great- Circle  Sailing.) 

CONSTELLATION.— A  group  of  stars  to  which  is  given 
the  name  of  some  classical  hero,  beast,  bird,  fish,  figure,  etc. 
The  Pole  Star  is  in  the  constellation  of  Ursa  Minor  (The  Little 
Bear),  and  the  Dipper  is  in  the  constellation  of  Ursa  Major  (The 
Great  Bear),  etc.  (See  Fixed  Stars  ;  Planets.) 

CORRECTED  ALTITUDE.— The  observed  altitude  of  a 
heavenly  body,  with  allowances  made  for  dip,  refraction,  etc. 
(See  Eighty-lSTine-Forty-Eight.) 

Sun — If  the  altitude  of  the  sun's  lower  limb  is  measured,  the 
semidiameter  (Nautical  Almanac)  must  be  added,  but  if  the 
upper  limb  is  observed,  the  semidiameter  must  be  subtracted, 
in  order  to  obtain  the  altitude  of  the  sun's  centre  from  the  hori- 
zon. For  practical  purposes  the  semidiameter  of  the  sun  may 
be  called  16'. 

Parallax  (Table  16)  is  always  added,  because  the  body  appears 
lower  when  viewed  from  the  surface  of  the  earth  than  it  would 
if  observed  from  the  earth's  centre — except  when  the  body  is  in 
the  observer's  zenith  when  it  has  no  parallax. 

Dip  (Table  14)  is  always  subtracted,  as  the  elevation  of  the 
observer's  eye  above  the  sea-level  causes  the  navigator  to  meas- 
ure too  great  an  altitude. 

Refraction  (Table  20)  is  always  subtracted,  owing  to  the  body 


THE  NAVIGATOR'S  POCKET-BOOK  41 

being  seen  above  its  true  place,  except  when  it  is  in  the  zenith 
of  the  observer,  when  it  has  no  refraction. 

Moon. — The  semidiameter  (Nautical  Almanac)  of  the  moon 
and  the  dip  (Table  14)  are  applied  in  exactly  the  same  manner  as 
explained  for  the  sun  ;  but  parallax  in  the  case  of  the  moon  is 
large  as  compared  with  refraction,  and  it  is  so  arranged  that  the 
moon's  parallax  (Table  24)  is  given  minus  the  refraction,  so  that 
the  figures  selected  from  this  table  must  always  be  added  to  the 
altitude.  For  practical  purposes  the  semidiameter  of  the  moon 
may  be  called  16',  the  same  as  the  sun. 

Planets — The  altitudes  of  these  bodies  are  corrected  for 
dip  (Table  14)  and  refraction  (Table  20)  as  usual,  but  the  correc- 
tion for  parallax  involves  a  new  process.  With  the  planet's  hori- 
zontal parallax  (Nautical  Almanac)  and  the  observed  altitude, 
find  the  planet's  parallax  (Table  17)  by  applying  the  first  two 
quantities  in  their  respective  columns.  The  semidiameters  of 
the  planets  are  given  in  the  almanac,  and  if  used  must  be 
applied  as  usual,  but  it  is  to  be  explained  that  for  practical  pur- 
poses the  altitude  of  a  planet  is  never  corrected  for  semidiam- 
eter and  parallax. 

Stars.— The  altitudes  of  the  stars  are  corrected  for  dip  (Table 
14)  and  refraction  (Table  20)  as  usual  ;  they  have  no  apparent 
diameter  or  parallax. 

Recapitulation. — Note  the  following: 

Semidiameter  is  always  added  for  the  lower  limb  and  sub- 
tracted for  the  upper  limb. 

Parallax  is  always  added. 

Dip  is  always  subtracted. 

Refraction  is  always  subtracted. 

It  is  to  be  remembered  that  the  sextant's  index  error  (if  it  has  any) 
is  always  to  be  figured  as  an  altitude  correction  (See  Sextant.) 


42  THE  NAVIGATOR'S  POCKET-BOOK 

CORRECTED  COURSE. — As  a  preliminary  to  working 
out  a  ship's  position  by  dead-reckoning,  the  compass  courses 
that  have  been  sailed  are  converted  into  true  or  geographical 
courses  by  correcting  them  for  leeway,  deviation,  and  varia- 
tion. 

Leeway. — The  amount  is  determined  as  explained  under  the 
head  of  Leeway,  and  this  quantity  is  allowed  to  leeward  of  the 
compass  course.  For  example,  if  the  course  sailed  was  east 
and  the  vessel  was  on  the  starboard  tack  making  one  point  of 
leeway,  the  same  must  be  allowed  toward  the  north,  making  the 
so  far  corrected  course  east- by-north. 

Deviation. — Westerly  deviation  must  be  allowed  away  from 
the  compass  course  in  a  direction  contrary  to  the  way  that  the 
hands  of  a  watch  revolve.  For  instance,  if  the  course  after  be- 
ing corrected  for  leeway  is  east-by-north,  and  there  is  one  point 
of  westerly  deviation  to  be  considered,  the  same  must  be  allowed 
toward  the  north,  making  the  correct  magnetic  course  east- 
northeast.  On  the  other  hand,  easterly  deviation  will  be  al- 
lowed away  from  the  compass  course  in  a  direction  the  same 
as  the  hands  of  a  watch  revolve.  To  illustrate  :  if  the  course  is 
east-by-north,  and  there  is  one  point  of  easterly  deviation  to  be 
considered,  the  same  must  be  allowed  toward  the  east,  making, 
in  this  case,  the  course  east. 

Variation.— This  is  allowed  in  exactly  the  same  way  as 
explained  for  deviation,  as  will  be  seen  following  :  we  will  say 
that  the  compass  course  after  being  corrected  for  leeway  and 
deviation  is  east-north-east,  and  that  there  is  one  point  of  west- 
erly variation  to  be  considered.  In  this  case  the  true  or  geo- 
graphical track  that  the  ship  has  made  is  northeast-by-east. 

Again,  suppose  that  the  compass  course  after  being  corrected 
for  leeway  and  deviation  is  east,  and  that  there  is  one  point  of 


THE  NAVIGATOR'S  POCKET-BOOK  43 

easterly  variation  to  be  considered.  In  this  case  the  true  or 
geographical  track  that  the  ship  has  made  is  east- by-south. 

Remarks. — When  the  variation  and  deviation  are  of  the  same 
name  (both  east  or  both  west)  they  may  be  added  together  and 
applied. 

If  the  variation  and  deviation  are  of  contrary  names  they  may 
be  subtracted  one  from  the  other  and  the  balance  applied  in  the 
name  of  the  greater  of  the  two  quantities. 

It  is  to  be  explained  that  leeway  made  on  the  starboard  tack 
is  applied  in  the  same  direction  as  westerly  variation  and  devia- 
tion, and  that  leeway  made  on  the  port  tack  is  applied  in  the 
same  direction  as  easterly  variation  and  deviation  ;  consequently 
there  are  times  when  the  three  quantities  of  leeway,  variation, 
and  deviation  may  be  added  together  and  applied  as  a  whole  to 
a  compass  course. 

CORRECTED  LOCAL  TIME — To  ascertain  the  correct 
local  time  at  the  ship,  proceed  as  follows  :  to  the  sun's  time 
shown  by  tue  ship's  clock  (set  when  the  sun  crossed  the  ship's 
meridian)  add  four  minutes  for  every  degree  of  longitude  sailed 
east  since  the  clock  was  last  set,  but  subtract  four  minutes  for 
every  degree  sailed  west ;  the  answer  will  be  the  local  apparent 
time  at  ship. 

COURSE  AND  DISTANCE.— (See  Chart  Sailing ;  Great- 
Circle  Sailing  ;  Mercator's  Sailing  ;  Middle  Latitude  Sailing.) 

COURSE  MADE  .GOOD.— The  bearing  of  the  vessel  from 
the  latitude  and  longitude  last  determined,  irrespective  of  the 
traverse  sailed.  (See  Dead-Reckoning.) 

COURSE  PROTRACTOR.— This  consists  of  a  half  circle  of 
thin  horn  or  isinglass,  having  its  circular  edge  graduated  into 
degrees,  and  a  long  thread  leading  from  the  centre  of  the  instru- 


44  THE  NAVIGATOR'S-  POCKET-BOOK 

meut.  To  ascertain  the  course  by  this  little  contrivance  place 
its  zero  line  on  any  convenient  meridian  on  the  chart,  then  slide 
it  up  or  down  on  this  true  north  and  south  line  until  the  thread 
lies  in  a  straight  line  over  the  position  of  the  ship  and  the  place 
sought.  The  course  between  the  two  points  will  be  indicated  in 
degrees  on  the  circle  by  the  direction  of  the  thread. 

Remarks. — The  course  protractor  always  gives  the  true  or 
geographical  course,  to  which  must  be  allowed  the  variation  of 
the  compass  for  the  locality  of  the  ship  in  order  to  convert  it  into 
a  magnetic  course.  If  deviation  exists  for  the  compass  course 
found,  then  this  quantity  must  also  be  applied.  (See  Chart 
Sailing.) 

CROSS-BEARINGS.— (See  Chart  Sailing.) 

CULMINATE.— When  a  heavenly  body  crosses  the  meridian 
of  the  observer  it  is  said  to  culminate.  Upper  culmination  is 
when  a  heavenly  body  crosses  the  meridian  above  the  pole, 
and  lower  culmination  is  when  it  crosses  the  meridian  below 
the  pole.  What  is  known  as  a  moon-culminating  star  is  one  that 
comes  to  the  meridian  at  the  same  time  with  the  moon. 

CURRENT. — A  progressive  motion  of  the  water  of  the  sea  at 
a  certain  place  ;  an  ocean  river.  The  flow  of  a  current  is  named 
according  to  the  direction  in  which  it  sets,  hence  a  northeast 
current  comes  out  of  the  southwest  and  flows  toward  the 
northeast.  (See  Patent  Log.) 

CURRENT  LOG.— Same  as  ground  log,  which  see. 

CURRENT  SAILING.— When  a  vessel  experiences  a  cur- 
rent, the  effect  is  to  set  her  in  the  direction  of  its  flow.  This 
must  be  considered  as  a  regular  and  separate  course,  and  the 
hourly  velocity  of  the  current  is  to  be  taken  as  the  rate  of  speed 
made  on  such  course,  as  shown  following : 


THE  NAVIGATOR'S  POCKET-BOOK  45 

Example. — A  ship  while  sailing  southeast  enters  the  Gulf 
Stream  at  a  point  where  it  is  flowing  northeast  at  the  rate  of  two 
knots  per  hour,  and  remains  in  the  stream  ten  hours.  This  data 
is  recorded  in  the  log-book,  and  when  working  out  the  dead- 
reckoning  this  course  of  northeast  must  be  entered  on  the  trav- 
erse table,  and  the  distance  of  twenty  miles  considered  as  the 
number  of  knots  sailed  on  that  course. 

Remarks. — The  chart  will  give  the  flow  of  the  current  either 
as  true  or  magnetic.  If  the  former,  no  correction  is  to  be  ap- 
plied to  it  after  entering  it  on  the  traverse  table  ;  but  if  the  latter, 
then  the  variation  must  be  applied  in  order  to  convert  it  into  a 
true  course.  The  deviation  of  the  compass  never  enters  into 
this  consideration,  because  the  direction  is  given  by  the  chart. 
(See  Patent  Log.) 

OUT. — When  referring  to  the  graduation  of  the  sextant  arc, 
it  is  said  to  be  cut  to  ten  minutes  (10'),  and  the  vernier  is  said  to 
be  cut  to  ten  seconds  (10"). 

CYCLONE — (See  Law  of  Storms.) 

DANGER  ANGLE.— (See  Chart  Sailing.) 

DANGER-ANGLE  TABLES.— Tables  that  give  by  mere 
inspection  the  distance  of  a  vessel  from  a  certain  object.  In  this 
consideration  the  known  height  of  the  lighthouse  and  the  verti- 
cal angle  of  the  same  measured  to  the  surface  of  the  water  are  all 
that  is  required  for  the  navigator  to  ascertain  his  distance  from 
the  object.  The  danger-angle  tables  found  in  the  back  of  this 
book  have  been  arranged  by  the  author  to  the  nearest  10"  of  arc 
(that  being  the  lowest  graduation  shown  on  sextants)  and  extend 
from  thirty  feet  to  three  hundred  and  twenty  feet.  The  manner 
of  using  these  tables  is  explained  under  the  head  of  Chart  Sail- 
ing. To  determine  the  distance  of  a  vessel  from  a  lighthouse 


46  THE  NAVIGATOR'S  POCKET-BOOK 

when  beyond  the  limit  of  the  figures  in  the  danger-angle  tables, 
the  "  Distance  "  table  in  the  back  of  this  book  may  be  employed. 

DARKS. — Having  reference  to  those  nights  during  which  the 
moon  is  not  seen  in  the  heavens. 

DAY.  —  (See  Astronomical  Day  ;  Circumnavigator's  Day ; 
Gained  Day  ;  Lost  Day  ;  Lunar  Day  ;  Sea  Day  ;  Sidereal  Day  ; 
Solar  Day.) 

DAY'S  WORK — The  calculation  of  the  ship's  latitude  and 
longitude  by  dead-reckoning. 

DEAD-RECKONING — The  position  of  the  ship  found  by 
referring  the  true  courses  to  the  nautical  tables  and  selecting  for 
each  course  the  respective  amounts  of  latitude  and  departure, 
then  applying  the  aggregate  value  of  these  to  the  latitude  and 
longitude  left.  The  manner  of  converting  compass  courses  into 
true  or  geographical  courses  is  explained  under  the  head  of 
Corrected  Course. 

To  Find  the  Latitude  and  Longitude. — Convert  the  compass 
courses  sailed  into  true  or  geographical  courses  by  applying  the 
leeway,  deviation,  and  variation.  With  the  distance  made  on 
each  course,  find  separately  (Table  1  or  2)  the  difference  of  lati- 
tude and  departure.  After  selecting  for  all,  foot  the  columns  of 
the  traverse  table,  and  if  both  northing  and  southing  have  been 
made  subtract  one  from  the  other  ;  also  if  both  easting  and  west- 
ing have  been  made  subtract  one  from  the  other. 

Apply  the  difference  of  latitude  to  the  latitude  left,  adding 
the  same  if  the  ship  has  sailed  toward  the  poles,  but  subtracting 
if  the  ship  has  sailed  toward  the  equator  ;  the  answer  will  be  the 
latitude  by  dead-reckoning. 

Next  turn  to  the  page  (Table  2)  marked  with  the  degrees  of  the 
middle  latitude,  apply  the  departure  in  the  latitude  column  (read- 


THE  NAVIGATOR'S  POCKET-BOOK  47 

ing  from  top  of  page  if  the  degrees  of  the  middle  latitude  were 
'found  there,  but  from  the  bottom  if  the  degrees  were  found 
there),  and  opposite  to  the  left  in  the  distance  column  will  stand 
the  difference  of  longitude.  Apply  this  latter  to  the  longitude 
left,  adding  the  same  if  the  longitude  has  been  increased,  but  sub- 
tracting if  the  longitude  has  been  decreased  ;  the  answer  will  be 
the  longitude  by  dead-reckoning. 

To  Find  the  Course  and  Distance — With  the  difference  of 
latitude  and  departure,  make  them  compare  (Table  2)  in  their 
respective  columns  opposite  each  other,  and  in  the  distance 
column  to  the  left  will  be  seen  the  distance  in  nautical  miles 
made  good,  and  the  true  or  geographical  bearing  (called  course 
made  good)  of  the  vessel  from  her  former  calculated  position 
will  be  read  in  degrees  from  the  top  of  the  page  if  the  difference 
of  latitude  is  greater  than  the  departure,  but  from  the  bottom  of 
the  page  if  the  departure  exceeds  the  difference  of  latitude. 

Remarks. — If  the  vessel  has  been  sailing  in  a  current,  or  has 
been  hove-to,  or  has  taken  farewell  from  the  land,  these  are  con- 
siderations for  the  traverse  table.  (See  Current  Sailing ;  Depart- 
ure ;  Drift.) 

Sailing-vessels  steer  by  quarter  points,  but  steamships  steer  by 
degrees,  consequently  in  the  former  sailing,  Table  1  is  employed, 
and  in  the  latter  sailing  Table  2  is  made  use  of. 

To  select  the  difference  of  latitude  and  departure,  apply  the 
distance  sailed  on  the  particular  course  in  the  column  marked 
"  Dist."  in  the  tables,  then  read  the  figures  in  the  two  right- 
hand  columns.  If  the  course  was  found  at  the  top  of  the  page 
the  latitude  and  departure  must  be  read  from  the  top  ;  but  if 
the  course  was  found  at  the  bottom  of  the  page  the  latitude  and 
departure  must  be  read  from  the  bottom. 

DECLINATION.— The  angular  distance  of  a  heavenly  body 


48  THE  NAVIGATOR'S  POCKET-BOOK 

north  or  south  of  the  equinoctial.  Declination  may  be  expressed 
as  celestial  latitude.  The  declinations  of  the  sun,  moon,  planets, 
and  stars  are  to  be  corrected  as  explained  following  : 

Sun. — Select  from  the  Nautical  Almanac  the  sun's  declination 
for  Greenwich  noon  of  the  Greenwich  date,  and  correct  this  for 
the  hourly  difference  of  declination  by  multiplying  the  latter 
by  the  number  of  hours  that  the  chronometer  showed  before  or 
past  noon  at  Greenwich  at  the  time  the  altitude  was  measured, 
and  either  add  this  correction  to  or  subtract  it  from  the  declina- 
tion given  for  Greenwich  noon,  according  as  the  declination  is 
increasing  or  decreasing.  The  idea  is  to  ascertain  the  distance 
of  the  sun  north  or  south  of  the  equator  at  the  time  of  observa- 
tion. (See  Inclination.) 

Moon — Convert  into  astronomical  time  and  date  the  Green- 
wich time  shown  by  chronometer  when  the  moon's  altitude  was 
observed,  calling  the  hours  numerically  from  one  to  twenty-four 
instead  of  referring  to  them  as  A.M.  and  P.M.  For  example, 
if,  when  the  observation  was  taken,  the  chronometer  showed 
Greenwich  civil  time  November  5th,  8  P.M.,  both  date  and  hour 
would  be  astronomical,  and  would  stand  as  such  ;  but  if  the 
chronometer  showed  Greenwich  civil  time  November  5th,  2 
A.M.,  then  call  the  astronomical  date  November  4th  and  the  time 
fourteen  hours.  (See  Astronomical  Time.) 

Now  turn  to  the  Nautical  Almanac,  and  under  the  astronomical 
date  and  opposite  the  astronomical  hour  select  the  moon's  dec- 
lination given.  Opposite  to  this  to  the  right  will  be  seen  the 
moon's  change  of  declination  for  one  minute  of  time.  Multiply 
this  minute  difference  by  the  number  of  minutes  over  the  even 
astronomical  hour,  and  if  the  moon's  declination  is  increasing 
add  the  correction  to  the  declination  given  for  the  hour  ;  but  if 
the  moon's  declination  is  decreasing  subtract  the  correction. 


THE  NAVIGATOR'S  POCKET-BOOK  49 

Planets. — The  declination  of  a  planet  is  given  for  Greenwich 
noon,  and  must  be  corrected  in  precisely  the  same  manner  as 
described  for  the  sun — the  hourly  difference  of  the  planet's  dec- 
lination being  multiplied  by  the  number  of  hours  shown  from 
Greenwich  noon  by  the  chronometer  at  the  time  of  observation, 
and  this  correction  either  added  to  or  subtracted  from  the  dec- 
lination of  the  planet  given  for  Greenwich  noon,  according  as 
the  planet's  declination  is  increasing  or  decreasing. 

Stars. — The  declinations  of  the  stars  being  practically  a  fixed 
quantity,  no  correction  is  necessary  for  the  declinations  given 
for  those  bodies— accepting  the  declinations  for  the  given  year 
as  shown  in  the  Nautical  Almanac  being  all-sufficient. 

DEGREE. — The  360th  part  of  the  circumference  of  a  circle. 
The  value  of  a  degree  is  60'.  A  degree  of  latitude  is  equal  to 
sixty  nautical  miles  or  knots,  anywhere  from  the  equator  to  the 
poles  ;  but  a  degree  of  longitude  is  equal  to  sixty  nautical  miles 
only  on  the  equator.  Leaving  the  equator,  the  distance  between 
the  meridians  constantly  contracts,  so  that  at  the  poles  there  is 
no  such  thing  as  longitude,  all  the  meridians  meeting  at  those 
points.  If  it  is  desired  to  learn  the  distance  between  any  two 
meridians  on  a  certain  parallel  of  latitude,  simply  open  the 
nautical  tables  (Table  2)  at  the  page  marked  with  the  parallel  in 
question,  then  opposite  the  figures  60  in  the  distance  column 
will  be  found  (to  the  right)  in  the  latitude  column  the  number 
of  miles  between  the  meridians. 

Examples. — On  the  parallel  of  40°  the  distance  between  the 
meridians  is  forty- six  nautical  miles  or  knots  ;  consequently,  if 
the  ship  started  from  the  longitude  of  74°  and  sailed  forty-six 
nautical  miles  east  on  the  parallel  of  40°,  she  would  reach  the 
longitude  of  73°. 


50  THE  NAVIGATOR'S  POCKET-BOOK 

On  the  parallel  of  47°  the  distance  between  the  meridians  is 
40.9  (forty  and  nine-tenths)  nautical  miles. 

DEMAGNETIZED  COMPASS.— A  compass  the  needle  of 
which  has  parted  with  its  magnetism. 

DEPARTURE — The  amount  of  easting  or  westing  made  by 
a  vessel  from  a  certain  point.  To  ' '  take  departure  "  is  to  ob- 
serve the  bearing  of  and  calculate  the  distance  of  the  vessel  from 
a  lighthouse  or  other  point  when  the  harbor  is  cleared  and  the 
rirst  course  set.  This  is  also  known  as  "  taking  farewell." 

Example.— Departure  is  taken,  Sandy  Hook  light  bearing 
west  by  compass,  distant  six  miles.  This  is  entered  as  a  mem- 
orandum in  the  column  of  remarks  in  the  log-book,  and  when 
working  up  the  dead-reckoning  the  navigator  must  set  down  in 
the  traverse  table,  as  a  regular  compass  course  and  distance 
sailed  by  the  ship,  east,  six  miles.  The  latitude  and  longitude  of 
Sandy  Hook  light  being  accepted  as  a  point  of  farewell,  the 
opposite  point  to  the  bearing  of  the  light  and  the  distance  from 
it  must  be  considered  as  having  been  sailed  ;  otherwise  the  ship 
would  be  six  miles  out  in  her  dead-reckoning. 

This  course  of  east  must  be  corrected  for  the  deviation  of  the 
compass  for  the  ship's  head  (if  deviation  exists),  also  for  the 
variation  of  the  compass  given  by  the  chart  for  the  locality  of 
the  vessel ;  this  will  convert  it  into  a  true  or  geographical  course. 
(See  Corrected  Course.) 

DEVIATION.-— (See  Compass ;  Amplitude  ;  Azimuth  ;  Cor- 
rected Course.) 

DIP. — A  heavenly  body  is  understood  to  dip  when  it  disap- 
pears below  the  horizon.  When  a  heavenly  body  crosses  the 
meridian  of  the  observer  the  limb  of  its  image,  as  viewed  in  the 


THE   NAVIGATORS   POCKET-BOOK  51 

sextant-glass,  will  drop  below  the  horizon  line,  and  under  such 
conditions  it  is  said  to  dip.     (See  Dipping  Needle.) 

DIP  OF  THE  HORIZON.— As  the  observer's  eye  is  natu- 
rally above  the  sea-level,  the  limit  of  view  is  called  the  visible  ov 
apparent  horizon,  and  the  angle  between  this  and  the  sensible 
horizon  is  called  the  dip  of  the  horizon,  which  is  further  ex- 
plained under  the  head  of  Corrected  Altitude.- 

DIPPER — The  seven  stars  forming  the  constellation  of  the 
Great  Bear,  and  by  means  of  which  the  Pole  Star,  in  the  tail  of 
the  Little  Bear,  can  be  readily  found. 

DIPPING  NEEDLE.— A  magnetic  needle  suspended  at  its 
centre  of  gravity  so  as  to  move  freely  from  the  horizontal  to  the 
perpendicular.  On  the  magnetic  equator  the  needle  assumes 
the  horizontal,  but  at  the  magnetic  poles  it  stands  perpendicular 
or  has  a  dip  of  90°. 

DISTANCE  TABLES.— Tabulated  distances  at  which  ob- 
jects can  be  seen  at  sea  according  to  their  respective  elevations, 
combined  with  the  height  of  the  observer's  eye  above  the  sea- 
level.  A  distance  table  will  be  found  in  the  back  of  this  book. 
{See  Danger- Angle  Tables.) 

DIURNAL.— Relating  to  the  day. 

DIURNAL  ARC.— The  half  circle  described  by  a  heavenly 
body  from  its  rising  to  its  setting.  (See  Nocturnal  Arc.) 

DIVIDERS. — An  instrument  consisting  of  two  pivoted  legs, 
used  by  navigators  for  measuring  distance  on  a  chant,  pricking 
off  positions,  etc. 

DOMESTIC  NAVIGATION.— Generally  refers  to  inland 
sailing. 


£2  THE  NAVIGATOR'S  POCKET-BOOK 

DOUBLE  ALTITUDE  PROBLEM.  —  (See  Sumner's 
Method.) 

DOUBLE  STAR. — Two  stars  appearing  so  close  together 
that  they  seem  to  touch. 

D.  R. — Letters  employed  to  express  the  word  dead-reckoning. 

DRIFT. — When  a  ship  is  hove-to  she  will  continually  come 
up  and  fall  off.  The  middle  point  between  this  coming  up  and 
falling  off  must  be  considered  as  her  compass  course,  and  the 
leeway,  deviation,  and  variation  applied  to  this  compass  course 
in  order  to  obtain  the  true  or  geographical  track  of  the  ship. 

Example. — A  ship  is  hove-to  on  the  starboard  tack  ;  her  head 
comes  up  to  east  and  falls  off  to  east-northeast ;  leeway,  four 
points  ;  deviation  of  the  compass,  one  point  westerly;  variation 
of  the  compass,  one  point  westerly. 

Now  the  middle  point  between  east  and  east-northeast  is  east- 
by-north,  and  to  this  we  apply  the  leeway,  which  gives  us 
northeast-by-north.  Next  we  apply  the  deviation  and  variation, 
and  obtain  for  the  true  or  geographical  course  of  the  ship  north- 
by-east. 

DRY  COMPASS.— A  compass  card  enclosed  in  an  air-cham- 
ber, commonly  referred  to  as  a  dry-card  compass.  (See  Liquid 
Compass.) 

DUMB  COMPASS. — A  circle  of  brass  or  other  substance 
having  engraved  or  printed  on  it  the  points  of  the  compass. 

EARTH. — The  third  planet  in  order  of  distance  from  the  sun  ; 
equatorial  diameter,  7,926  miles  ;  polar  diameter,  7,899  miles. 
The  difference  between  the  two  diameters  (twenty-seven  miles) 
is  called  the  compression.  Surface,  one  hundred  and  ninety- 
seven  millions  of  square  statute  miles,  of  which  fifty-one  mill- 
ions is  land  ;  mean  distance  from  the  sun,  ninety-three  millions 


THE  NAVIGATOR'S  POCKET-BOOK  53 

of  miles  ;  circumference  at  the  equator,  about  twenty-five  thou- 
sand miles  ;  inclination  to  the  plane  of  the  ecliptic,  23^°. 
EARTH'S  INDUCTION — (See  Magnetic  Induction.) 
EIGHTY-NINE-FORTY-EIGHT.  —  In  working  latitude 
some  navigators  lump  the  correction  for  the  lower  limb  of  the 
sun  as  a  constant  plus  12'  quantity,  and  simply  add  this  amount 
to  their  observed  altitude  in  order  to  obtain  the  central  altitude 
of  the  body.  They  then  subtract  the  latter  from  90°,  as  usual, 
to  find  the  zenith  distance.  Others  adopt  a  still  shorter  method 
for  obtaining  the  zenith  distance  :  instead  of  adding  12'  to  their 
observed  altitude  they  subtract  the  observed  altitude  from  89° 
48'  (which  is  12'  less  than  90°),  which  at  once  gives  the  zenith 
distance.  This  twelve-minute  or  eighty-nine-forty-eight  meth- 
od is  liable  to  make  an  error  of  several  miles  in  the  answer  to 
the  problem  when  the  height  of  eye  correction  (dip)  is  large, 
such  as  it  would  be  on  the  deck  and  bridge  of  a  vessel  with  a 
high  freeboard.  Altitudes  should  always  be  corrected  as  ex- 
plained under  the  head  of  Corrected  Altitude. 

ECLIPTIC.— The  apparent  path  of  the  sun  around  the  earth, 
but  the  earth's  real  path.  (See  Inclination.) 

ELEVATED  COMPASS. — A  masthead  or  a  pole  compass 
raised  above  the  deck  for  the  purpose  of  getting  it  beyond  the 
magnetic  influence  of  the  ship's  iron  and  machinery. 

ELEVATED  POLE.— The  pole  which  is  above  the  horizon. 
The  elevation  of  the  pole  is  the  altitude  of  the  pole  above  the 
true  horizon,  and  it  is  equal  to  the  latitude  of  the  place. 

EPHEMERIS. — An  unabridged  astronomical  almanac. 

EPITOME.— An  abridged  treatise,  such  as  an  epitome  of 
navigation. 


54  THE  NAVIGATOR'S  POCKET-BOOK 

EQUAL  ALTITUDES.— (See  Longitude.) 

EQUATION  OF  TIME.— The  difference  between  mean  and 
apparent  time.  The  equation  of  time  selected  from  the  Nautical 
Almanac  for  Greenwich  noon  of  the  given  Greenwich  date  must 
always  be  corrected  for  the  number  of  hours  shown  from  Green- 
wich noon  by  the  chronometer  when  the  altitude  of  the  heavenly 
body  was  measured. 

Rule.— Select  from  the  Nautical  Almanac  the  equation  of  time 
for  the  given  Greenwich  noon,  also  the  hourly  difference  of 
equation,  and  multiply  the  latter  by  the  number  of  hours  shown 
from  Greenwich  noon  by  the  chronometer  when  the  observation 
was  taken ;  then  either  add  this  correction  to  or  subtract  it 
from  the  equation  given  for  Greenwich  noon,  according  as  the 
equation  of  time  is  increasing  or  decreasing.  The  idea  is  to 
find  the  equation  of  time  for  the  hour  of  observation.  (See 
Mean  Sun.) 

EQUATOR.— The  imaginary  line  encircling  the  earth,  equi- 
distant 90°  from  the  north  and  south  poles. 

EQUINOCTIAL — The  celestial  equator. 
EQUINOCTIAL  POINTS.— (See  First  Point  of  Aries.) 
EQUINOX. — (See  Autumnal  Equinox  ;  Vernal  Equinox.) 
ERROR  OF  COLLIMATION.— (See  Axis  of  Collimation.) 
EVENING  STAR.— (See  Morning  Star.) 
EX-MERIDIAN.— (See  Latitude.) 
FAREWELL — (See  Departure.) 
FATHOM.— (Six  feet.) 
FINDING  THE  TIME.— (See  Regulating.) 


THE  NAVIGATOR'S  POCKET-BOOK  55 

FIRST  MERIDIAN.— (See  Prime  Meridian  ;  Circumnavi- 
gator's Day.) 

FIRST  POINT  OF  ARIES — That  point  of  the  ecliptic 
which  the  sun  crosses  on  March  21st  from  the  south  to  the 
north  side  of  the  equator.  The  point  of  the  ecliptic  which  the 
sun  crosses  on  September  23d  from  the  north  to  the  south 
side  of  the  equator  is  known  as  the  First  Point  of  Libra.  These 
two  points  are  termed  the  Equinoctial  Points,  and  when  the 
sun  crosses  them  the  lengths  of  the  days  and  nights  are  equal 
throughout  the  world.  The  First  Point  of  Aries  is  the  Spring 
(or  Vernal)  Equinox,  and  the  First  Point  of  Libra  is  the  Au- 
tumnal Equinox. 

FIRST  POINT  OF  CANCER — That  point  of  the  ecliptic 
which  the  sun  enters  about  June  21st,  when  its  declination  is 
23£°  north. 

FIRST  POINT  OF  CAPRICORN.  —  That  point  of  the 
ecliptic  which  the  sun  enters  about  December  21st,  when  its 
declination  is  23i°  south. 

FIRST  POINT  OF  LIBRA.— (See  First  Point  of  Aries.) 
FIXED  STARS.— The  term  "fixed  stars"  applies  to  those  bod- 
ies in  the  heavens  which  appear  constantly  in  the  same  relative 
position.  The  fixed  stars  shine  by  their  own  light,  and  their  ap- 
parent twinkling  and  their  smaller  appearance  distinguish  them 
from  the  planets.  The  planets  are  seen  sometimes  in  one  posi- 
tion and  sometimes  in  another,  the  same  planet  being  at  one 
time  the  morning  star  and  at  another  time  the  evening  star.  The 
fixed  stars  are  separated  into  classes,  the  brightest  being  stars  of 
the  first  magnitude,  of  which  it  is  generally  accepted  there  are 
nineteen  ;  the  second  in  order  of  brightness  are  classed  under 
the  head  of  second  magnitude  and  number  about  sixty  ;  next 


56  THE  NAVIGATOR'S  POCKET-BOOK 

the  third  magnitude,  numbering  about  two  hundred  ;  then  follow 
fourth,  fifth,  and  sixth  magnitudes,  beyond  which  they  cannot 
be  distinguished  without  the  aid  of  a  telescope,  consequently 
such  stars  are  known  as  telescopic  stars.  Variable  stars  are  those 
which  appear  to  intermit  in  the  way  of  brightness,  and  inter- 
mediate stars  are  those  which  are  divided  between  two  magni- 
tudes, and  may  be  seen  expressed  as  1-2,  meaning  that  they  are 
nearer  1  than  2  ;  but  if  they  are  expressed  as  2-1,  it  means  that 
they  are  nearer  2  than  1.  The  term  magnitude  has  no  reference 
to  the  dimensions  or  masses  of  the  stars,  but  only  to  their  bright- 
ness. The  word  constellation  means  a  group  of  stars,  fanci- 
fully supposed  to  represent  some  figure,  such  as  a  classical  hero, 
a  beast,  bird,  fish,  etc.  The  brightest  stars  were  distinguished 
by  the  ancient  astronomers  by  proper  names,  such  as  Rigel,  Sir- 
ius,  etc.;  but  the  commonest  practice  is  to  use  the  small  letters 
of  the  Greek  and  Roman  alphabets  to  classify  their  degrees  of 
brightness,  a  being  prefixed  to  the  brightest,  ft  to  the  next 
brightest,  and  so  on.  When  the  Greek  letters  are  exhausted  the 
Roman  are  made  use  of,  such  as  a,  b,  c,  d,  etc.,  and  when  these 
are  also  exhausted  then  numerals  are  made  use  of,  such  as  1,  2, 
3,  4,  etc. 

The  following  nine  stars  (Arietis,  Aldebaran,  Pollux,  Regulus, 
Spica,  Antares,  Aquilse,  Fomalhaut,  and  Pegasi)  are  those  prin- 
cipally used  by  navigators  for  finding  the  longitude,  arid  the 
navigator  should  not  rest  satisfied  until  he  has  succeeded  in  so 
familiarizing  himself  with  those  parts  of  the  heavens  in  which 
they  are  placed  as  to  be  able  to  readily  refer  to  them.  By  fol- 
lowing the  directions  given  he  may  soon  impress  their  relative 
positions  upon  his  memory. 

In  the  higher  northern  latitudes  if  the  observer  will  look 
toward  the  north  pole  he  will  see  (as  shown  following)  a  star 


THE  NAVIGATOR'S  POCKET-BOOK  57 

*  of  the  second  magnitude,  called  the  Pole  Star.     It 

is  easily  recognized  because  it  has  no  other  star  of 

*  equal  brightness  in  its  immediate  vicinity,  and  be- 
*  *  *#  *     cause  it  is  always  seen  in  the  same  direction— bear- 
ing north.     Another  distinguishing  feature  in  rela- 
tion to  it  is  the  constellation  of  the  Seven  Stars, 
commonly  known  as  the  Dipper,  the  two  stars  in 
the  dipper  end  of  which  (called  the  Pointers)  point 
to  the  Pole  Star. 

a  Arietis.  This  star  bears  about  west,  distant  23°  from  the 

^.  Seven  Stars ;  it  is  of  the  second  magnitude,  and 

may  be  known  by  means  of  a  star  of  the  third  magni- 
tude, situated  southwest  from  a  Arietis,  at  the  dis- 

*  tance  of  3£°.     South  from  this  star,  at  a  distance  of 

*  1|°,  is  a  star  of  the  fourth  magnitude. 

Aldebaran.  ^  About  35°  east-southeast  from  a  Arietis,  and  14° 
southeast  from  the  Seven  Stars,  is  the  bright  star 
**  *  Aldebaran.  Near  this  star  to  the  westward  are  sev- 
eral stars  of  the  third  and  fourth  magnitudes,  form- 
ing with  Aldebaran  the  letter  V.  At  the  distance 
of  23°  from  this  star,  in  a  southeast  direction,  are 
three  very  bright  stars,  situated  in  a  straight  line, 
near  to  each  other,  being  known  as  The  Belt  of 
Orion. 

At  a  distance  of  45°  from  Aldebaran,  in  the  di- 
« 

rection  of  east-northeast,  is  the  bright  star  Pollux. 
Northwest  from  Pollux,  distant  5°,  is  the  bright 
star  Castor. 

East-southeast-half-east  from  Pollux,  at  a  dis- 
tance of  37}°,  is  the  bright  star  Regulus.    North  of 


58  THE  NAVIGATOK'S  POCKET-BOOK 

*  #        this  star,  at  a  distance  of  8°,  is  a  star  of  the  second 
#  magnitude,  and  further  to  the  northward  are  five 

*  stars  of  the  third  magnitude,  the  whole  forming  a 

*  cluster  resembling  a  sickle,  Regulus  being  the  ex- 
Regulus.  *      tremity  of  the  handle.     A  line  drawn  from  the 

Pole  Star,  through  its  pointers,  will  pass  about  12° 
to  the  eastward  of  Regulus. 

*  Spica.  East-southeast  from  Regulus,  at  a  distance  of  54°, 

is  the  bright  star  Spica,  with  no  other  bright  star 
near  it.  Southwest  from  this  star,  at  a  distance  of 
about  16°,  are  five  stars  of  the  third  and  fourth 
*  *  magnitudes,  situated  as  shown  in  adjoining  figure, 
the  two  northernmost  of  which  form  a  straight  line 
with  Spica. 

East-southeast  from  Spica,  at  a  distance  of  46°, 
is  the  remarkable  star  Antares,  being  of  a  reddish 

*  color,  so  that  it  is  easily  distinguishable.     On  each 
*  Antares.    side  of  it,  about  2°  distant,  is  to  be  found  a  star  of 

the  fourth  magnitude,  these  stars  bearing  respect- 
ively  from    Antares    west-northwest  and  south- 
southeast.     In  the  vicinity  of  Antares  there  is  no 
very  bright  star. 
Northeast  from  Antares,  at  the  distance  of  60°, 

*  is  the  bright  star  a  Aquilae  ;   north-northwest  of 
*a  Aquilae.  wm?cll>  at  2°  distant,  is  a  star  of  the  third  magni- 

K  tude,  and  south-southeast,  at  3°  distant,  is  a  star 

of  the  fourth  magnitude.  These  three  stars  ap- 
pear practically  in  a  straight  line,  a  Aquilae  may 
be  readily  distinguished,  as  it  is  of  a  reddish  nature, 
being  nearly  of  the  same  color  as  Antares. 


THE  NAVIGATOR'S  POCKET-BOOK  50 

Southeast  from  a  Aquilae,  at  a  distance  of  60°,  is 

the  bright  star  Fomalhaut.     It  is  in  high  southern 

Fomalhaut        declination,  so  that  in  northern  latitudes  its  altitude 

is  small.     On  the  parallel  of  40°  north  its  altitude 

is  about  20°.     Fomalhaut  bears  nearly  south  from 

#  the  star  a  Pegasi,  being  about  45°  distant.     A  line 
drawn  from  the  pointers  in  the  Dipper,  through  the 
Pole  Star,  and  continued  to  the  opposite  meridian, 
will  pass  very  near  to  a  Pegasi  and  Fomalhaut. 

East-by-north  from  a  Aquilae,  at  a  distance  of  48°, 
*    and  westward  from  aArietis,  at  a  distance  of  44°, 

*  is  the  star  a  Pegasi,  which  may  be  distinguished  by 

#  means  of  four  stars  of  varying  magnitudes,  situated 
*        as  shown  in  the  adjoining  figure.     The  star  due 

north  of  a  Pegasi  is  of  the  second  magnitude,  and 

#  a  Pegasi.    is  distant  13°.      The  two  close  stars  northwest  of 

a  Pegasi  point  to  this  star,  and  the  most  northern 
one  of  the  two  close  stars  is  in  line  with  a  Pegasi 
and  the  most  northern  and  western  star  in  the 
group. 

Remarks.—  To  reconcile  compass  directions  with  the  fore- 
going star  diagrams,  the  navigator  must  hold  the  page  upside 
down  over  his  head,  directing  the  top  of  the  page  toward  the 
north. 

FOCAL  DISTANCE. — The  distance  between  the  object-glass 
and  the  image.  Focal  length  means  the  same  as  focal  distance. 

FOUR-POINT  BEARING.— (See  Chart  Sailing.) 

FURLONG.— An  eighth  of  a  mile  ;  =  forty  rods  ;  =  two 
hundred  and  twenty  yards  ;  =  six  hundred  and  sixty  feet. 


60  THE  NAVIGATOR'S  ^POCKET-BOOK 

GAINED  DAY.— (See  Circumnavigator's  Day.) 

GEOGRAPHICAL  MILE.— A  nautical  or  sea  mile  of 
6,082.66  feet ;  the  mean  length  of  a  minute  of  latitude  ;  a  knot. 

GEOGRAPHICAL  POLES — The  extremities  of  the  earth's 
axis  ;  the  two  points  of  90°  north  and  south. 

GRADUATED. — Divided ;  a  scale,  as,  for  instance,  the  grad- 
uated arc  of  a  quadrant,  octant,  and  sextant,  or  a  graduated 
vernier. 

GRADUATED  RULES.— Parallel  rules  having  one  of  the 
bevelled  edges  divided  into  degrees  and  the  other  edge  divided 
into  quarter  points  of  the  compass.  They  are  used  for  shaping 
a  course  and  are  independent  of  the  diagram  compasses  on  the 
chart. 

Rule. — Lay  the  rules  on  the  chart  on  the  course  to  be  deter- 
mined so  that  the  centre  mark  of  the  rules  rests  on  a  meridian 
line,  and  read  the  true  course  on  the  divided  edge  where  it  is  cut 
by  the  meridian  line.  This  true  course  must  always  have  the 
variation  of  the  compass  for  the  ship's  locality  applied  to  it  in 
order  to  convert  it  into  a  correct  magnetic  course  ;  and  provided 
deviation  of  the  compass  exists,  this  quantity  must  also  be  taken 
into  consideration.  (See  Chart  Sailing.) 

GREAT-CIRCLE  CHART.— (See  Chart.) 

GREAT-CIRCLE  SAILING. — A  straight  course  between 
two  places  is  the  arc  of  a  great  circle.  A  great-circle  track 
drawn  on  a  Mercator's  chart  represents  a  curve,  except  on  the 
meridians  and  on  the  equator,  which  are  great-circle  tracks  of 
themselves.  According  to  a  great-circle  track  plotted  on  a 
Mercator's  chart  a  ship  in  following  it  would  constantly  change 
the  direction  of  her  head,  but  in  reality  she  would  sail  in  a 


THE  NAVIGATOR'S  POCKET-BOOK  61 

straight  line.  This  is  to  be  explained  by  stating  that  a  Merca- 
tor's  chart  gives  a  distorted  view  of  the  earth's  surface. 

When  a  vessel,  as  in  the  case  of  a  steamship,  is  navigated  on 
a  straight-line  course  on  a  Mercator's  chart  her  head  is  never 
pointed  in  the  exact  direction  of  the  port  to  which  she  is  bound 
until  that  port  heaves  into  sight ;  but  when  following  a  great- 
circle  track  her  head  is  from  first  to  last  pointed  direct  for  her 
destined  port.  In  other  words,  when  a  vessel  is  navigated  on  a 
straight-line  course  on  a  Mercator's  chart,  her  head  at  starting 
points  toward  the  equatorial  side  of  the  port  bound  to,  and 
gradually,  as  the  voyage  progresses,  her  head  turns  in  the  right 
direction,  or  toward  the  point  of  her  destination  ;  whereas  the 
great-circle  track  leads  direct  from  one  port  to  the  other. 

As  well  as  shortening  the  distance  between  two  places,  the 
great-circle  track  is  of  the  highest  importance  for  sailing  ships, 
as  it  often  happens  that  a  more  or  less  head  wind  according  to  a 
Mercator's  course  is  made  a  fair  wind  on  a  great-circle  course. 
The  real  direction  of  the  port  bound  to  can  only  be  ascertained  by 
consulting  the  great  circle,  and  this  determines  whether  the  exist- 
ing wind  is  fair  or  ahead  for  the  great-circle  course. 

To  illustrate  the  foregoing  theory  the  author  shows  the  follow- 
ing example,  given  by  Captain  S.  T.  S.  Lecky,  in  his  masterly 
digest  of  navigation  entitled  "Wrinkles."  It  proves  the  possi- 
bilities of  the  great-circle  track  for  sailing  vessels  : 

Example. — "Take,  for  instance,  the  case  of  a  vessel  bound 
from  Quebec  to  Greenock  or  Liverpool.  The  true  course  and 
distance  by  Mercator's  chart  from  Belleisle  Light-house  to  Inish- 
trahul  Light-house  is  N.  83°  E.,  1,722  miles  ;  but  the  distance  on 
the  great  circle  is  1,690  miles,  or  thirty-two  miles  less ;  whilst 
the  course  at  starting  is  N.  63|°  E. ,  or  19|°  more  to  the  north- 
ward. Now  if  a  sailing  ship  on  clearing  the  Strait  has  the  wind 


62  THE  NAVIGATOR'S^  POCKET-BOOK 

at  east-half-north,  it  would  at  first  seern  immaterial  on  looking 
at  Mercator's  chart  which  tack  she  was  put  upon  ;  but  if  placed 
on  the  starboard  tack  she  would  lie  up  within  3£  points  of  the 
true  direction  of  her  port,  whilst  if  placed  on  the  other  tack, 
instead  of  approaching  her  port  she  would  be  actually  going 
away  from  it." 

To  Draw  the  Great-Circle  Track.— Professor  Airy's  exceed- 
ingly simple  and  valuable  table  for  sweeping  an  arc  of  a  great 
circle  on  a  Mercator's  chart  on  one  side  of  the  equator  is  given 
following,  and  is  heartily  indorsed  by  the  author  of  this  volume. 

Join  the  place  of  the  ship  and  the  place  of  destination  by  a 
straight  line  and  find  the  middle  point. 

Draw  from  this  middle  point  a  perpendicular  line  toward  the 
equator  and  continue  the  line  beyond  the  equator  if  found  neces- 
sary in  order  to  sweep  the  arc. 

With  the  middle  latitude  between  the  two  places  enter  the 
following  table  and  take  out  the  "  corresponding  parallel." 

The  resting-point  for  the  sharp  leg  of  the  pencil-point  dividers 
will  be  the  intersection  of  the  corresponding  parallel  with  the 
perpendicular  line.  Place  the  sharp  point  of  the  dividers  in 
this  intersection,  then  with  the  pencil  leg  of  the  instrument 
sweep  an  arc  that  will  pass  through  the  place  of  the  ship  and 
the  place  of  destination,  and  this  curved  line  will  be  the  great- 
circle  track  required. 

Changing  the  Course. — Except  on  the  meridians  and  on  the 
equator  a  ship  must  frequently  change  her  course  in  order  to 
keep  to  the  great  circle.  Several  points  on  the  arc  of  the  greaf 
circle  are  fixed  upon,  and  these  are  made  successively  by  the 
ship,  the  course  being  changed  with  each  point  arrived  at. 
These  courses  will  be  shaped  as  usual  by  the  parallel  rules  and 
the  diagram  compasses  on  the  chart,  so  that  in  reality  a  series  of 


THE  NAVIGATOR'S  POCKET-BOOK 


63 


Middle 
Latitude. 

Corresponding  Parallel. 

Middle 
Latitude. 

Corresponding  Parallel. 

Opposite  Name  to  Lat- 
itude of  Places. 

Same  Name  as  Lati- 
tude of  Places. 

20° 

81°  13' 

* 

* 

22° 

78°  16' 

* 

* 

24° 

74°  59' 

* 

* 

26° 

71°  26' 

* 

* 

28° 

67°  38' 

58° 

4°  00' 

30° 

63°  37' 

60° 

9°  15' 

82° 

59°  25' 

62° 

14°  32' 

34° 

55°  05' 

64° 

19°  50' 

36° 

50°  36' 

66° 

25°  09' 

38° 

46°  00' 

68° 

30°  30' 

40° 

41°  18' 

70° 

35°  52' 

42° 

36°  31' 

72° 

41°  14' 

44° 

31°  38' 

74° 

46°  37' 

46° 

26°  42' 

76° 

52°  01' 

48° 

21°  42' 

78° 

57°  25' 

50° 

16°  39' 

80° 

62°  51' 

52° 

11°  33' 

* 

* 

54° 

6°  24' 

* 

* 

56° 

1°  13' 

* 

* 

rhumb  lines  are  employed  by  the  navigator  to  enable  him  to 
keep  his  ship  approximately  on  the  great  circle. 

The  sum  of  the  distances  sailed  on  these  short  courses  will 
not  differ  much  from  the  distance  found  for  the  great  circle, 
provided  the  points  are  not  too  widely  spaced.  A  very  prac- 
tical method  employed  is  to  find  the  change  of  course  in  points 
of  the  compass  from  the  starting-place  to  the  middle  point  on 
the  arc  of  the  great  circle,  then  to  turn  this  number  of  points 


64  THE  NAVIGATOR'S  .POCKET-BOOK 

into  quarters,  and  divide  the  distance  of  half  the  circle  by  the 
number  of  quarter  points  so  obtained,  which  will  give  the  num- 
ber of  miles  to  sail  on  each  quarter  point. 

Example. — Suppose  that  between  the  starting-point  of  the 
great  circle  and  the  middle  part  of  same  the  change  of  course 
is  two  compass  points,  and  that  half  of  the  entire  length  of  the 
great-circle  track  is  1,000  miles.  Now  in  two  points  there  are 
eight  quarters,  so  we  divide  1,000  by  8  and  get  125  for  an  an- 
swer ;  consequently  we  should  change  the  course  a  quarter  of  a 
point  for  each  125  miles  sailed. 

The  navigator  should  bear  in  mind  that  the  deviation  of  the 
compass  must  be  considered  in  shaping  the  various  courses  on 
the  great-circle  track. 

Measuring  the  Distance.— Turn  the  largest  course  on  the 
great  circle  (which  will  be  one  of  the  ends  of  the  arc)  into  de- 
grees, and  proceed  as  follows :  Select  the  logarithms,  cosecant 
of  the  largest  course  angle,  cosine  of  the  smallest  latitude,  and 
the  sine  of  the  difference  of  longitude  between  the  two  places  ; 
add  these  three  logs  together,  reject  ten  in  the  index,  and  the  re- 
sult will  be  the  sine  of  the  distance — the  degrees  of  which  will 
be  multiplied  by  60  to  reduce  them  to  miles,  and  the  minutes  of 
the  angle  added  in,  and  the  result  will  be  the  distance  on  the 
great  circle. 

When  an  angle  exceeds  90°,  its  supplement  (what  it  lacks  of 
180°)  may  be  used,  but  in  this  case  the  sine  of  the  distance  should 
be  subtracted  from  180°,  and  the  answer  multiplied  by  60  to 
obtain  the  distance. 

Examples. — In  the  first  consideration,  with  a  course  of  80°  30', 
a  latitude  of  40°  30',  and  a  difference  of  longitude  of  60°  23', 
we  would  obtain  a  distance  of  2,525  miles. 
In  the  second  consideration,  with  a  course  of  55°  57',  a  lati- 


THE  NAVIGATOR'S  POCKET-BOOK  65 

tude  of  6°  48',  and  a  difference  of  longitude  of  140°  11',  we 
would  obtain  a  distance  of  7,793  miles. 

Remarks. — By  mere  inspection  it  is  possible  to  at  once  deter- 
mine if  a  great-circle  route  is  practicable — that  land,  ice,  etc., 
will  not  interfere. 

Great-circle  sailing  is  valuable  only  in  latitudes  beyond  the 
tropics,  as  within  them  (23°  N.  to  23°  S.)  the  difference  between 
the  great  circle  and  Mercator's  tracks  is  too  small  to  be  consid- 
ered— within  a  few  degrees  of  the  equator  all  straight  lines 
drawn  on  a  Mercator's  chart  practically  represent  great-circle 
tracks. 

What  is  known  as  Mixed  or  Composite  tracks  are  modifica- 
tions of  the  great-circle  track,  adopted  by  reason  of  obstacles  in 
the  way  of  the  latter,  such  as  land,  etc. 

When  driven  a  considerable  distance  from  the  great-circle 
track,  the  navigator  should  not  attempt  to  regain  it,  but  should 
trace  a  new  great  circle  from  the  place  of  the  ship. 

GREENWICH  DATE.— The  day  of  the  month  at  Green- 
wich. If  at  any  time  there  should  be  uncertainty  concerning 
the  Greenwich  date  it  may  be  determined  as  follows : 

Express  the  ship's  time  astronomically  (see  Astronomical 
Time),  then  turn  the  ship's  longitude  into  time  (see  Table  7,  or 
Arithmetic  of  Navigation),  and  proceed  according  to  one  of  the 
two  rules  given  below  : 

West  Longitude — Add  the  longitude  in  time  to  the  ship's  as- 
tronomical time  :  their  sum,  if  less  than  twenty-four  hours,  will 
be  the  Greenwich  time  of  the  same  date  as  at  ship  ;  but  if  their 
sum  is  greater  than  twenty-four  hours,  reject  twenty-four  hours 
and  put  the  Greenwich  date  one  forward. 

East  Longitude.— If  the  longitude  in  time  is  less  than  the 
ship's  astronomical  time,  subtract  the  former  from  the  latter, 
5 


66  THE  NAVIGATOR'S  .POCKET-BOOK 

and  call  the  Greenwich  date  the  same  as  the  ship's  date  ;  but  if 
the  longitude  in  time  is  greater  than  the  ship's  astronomical  time, 
add  twenty-four  hours  to  the  latter,  then  subtract,  and  call  the 
Greenwich  date  one  day  less  than  the  ship's  date. 

GREENWICH  TIME — The  Greenwich  hour  shown  by  a 
chronometer  set  to  that  meridian.  If  the  ship's  longitude  is 
turned  into  time  (see  Table  7,  or  Arithmetic  of  Navigation)  and 
added  to  the  local  time  at  the  vessel  (as  shown  by  the  ship's 
clock),  when  in  west  longitude,  but  subtracted  from  the  local 
time  at  ship  when  in  east  longitude,  the  answer  will  be  the 
Greenwich  time,  independent  of  the  chronometer. 

GROUND  LOG. — An  instrument  for  detecting  the  presence 
of  a  current  when  the  ship  is  becalmed  on  soundings  out  of 
sight  of  land.  An  ordinary  heaving  lead  is  made  fast  to  the 
regular  chip  log- line,  then  the  lead  is  cast  overboard  and  al- 
lowed to  rest  on  the  bottom.  If  there  is  a  current,  the  drift  of 
the  ship  from  the  lead  will  at  once  give  its  direction  by  the 
angle  of  the  log-line,  and  the  velocity  of  the  current  will  be 
measured  by  the  seconds  glass,  or  watch,  as  explained  under  the 
heading  of  Chip  Log. 

GUNTER'S  SCALE — A  flat  rule  about  two  feet  in  length, 
marked  on  one  side  with  the  scales  of  equal  parts,  chords,  tan- 
gents, sines,  etc.,  and  on  the  other  side  with  the  logarithms  of 
these  parts.  It  is  employed  for  solving  mechanically  certain 
problems  in  navigation  and  surveying. 

HACK  WATCH. — A  common  watch  used  by  navigators, 
who  set  it  to  the  time  shown  by  the  chronometer,  so  as  to  carry 
*he  Greenwich  time  with  them  on  deck  when  about  to  measure 
an  altitude.  It  is  also  set  to  the  apparent  time  at  ship  when  ob- 


THE  NAVIGATOR'S  POCKET-BOOK  6? 

serving  azimuth  bearings  of  the  sun  for  determining  the  devia- 
tion of  the  compass. 

HEAVE  OF  THE  SEA — When  a  vessel  is  sailing  more  or 
less  in  the  trough  of  a  heavy  sea,  the  effect  is  to  drive  her  to 
leeward,  and  this  is  expressed  either  as  the  heave  of  the  sea  or 
send  of  the  sea.  It  goes  without  saying  that  a  shallow  vessel 
will  be  lifted  off  more  than  a  deep  vessel,  and  for  that  reason  no 
rule  can  be  given,  the  navigator  being  obliged  from  experience 
to  estimate  the  quantity  for  his  vessel. 

HEELING  ERROR.— The  change  of  compass  deviation 
owing  to  the  vessel  being  listed  to  port  or  starboard,  and  which  is 
compensated  by  a  vertical  steel  magnet  placed  exactly  under  the 
centre  of  the  compass  card.  Heeling  error  will  be  at  its  maxi- 
mum when  the  vessel  is  heading  north  or  south,  as  the  north  end 
of  the  needle  will  be  drawn  to  the  elevated  (weather)  side. 

HIGH  LATITUDES. — Parallels  far  removed  from  the  equa- 
tor, both  in  the  northern  and  southern  hemispheres.  Opposed 
to  low  latitudes,  which  are  parallels  in  the  vicinity  of  the  equator. 

HORIZON — The  apparent  meeting  of  the  sea  and  sky.  (See 
Artificial  Horizon  ;  Dip  of  the  Horizon  ;  Sensible  Horizon  ;  Vis- 
ible Horizon.) 

HORIZON  GLASS.— (See  Sextant.) 

HORIZONTAL  DANGER  ANGLE.— (See  Chart  Sailing.) 

HORIZONTAL  PARALLAX.— When  a  heavenly  body 
is  on  the  horizon  of  the  observer,  its  altitude  to  him  is  practi- 
cally zero,  but  another  observer  viewing  the  body  at  the  same 
time  from  the  centre  of  the  earth  would  not  see  it  on  his  horizon, 
but  elevated  above  it ;  and  the  difference  between  these  two 
angles  is  called  the  horizontal  parallax. 


68  THE  NAVIGATOR'S  POCKET-BOOK 

HOUR  ANGLE.— The  angle  of  a  heavenly  body  at  the  pole, 
between  the  observer's  meridian  and  the  circle  of  declination  pass- 
ing through  the  body.  This  angle  is  measured  on  an  arc  of  the 
equinoctial  intercepted  between  the  meridian  and  the  circle  of 
declination,  and  is  converted  into  time  by  giving  to  every  fifteen 
degrees  (15°)  a  value  of  one  hour. 

HURRICANE — (See  Law  of  Storms.) 
HYDROGRAPHIO  CHART.— (See  Chart.) 

HYGROMETER.  —  A  wet-bulb  thermometer  employed  by 
navigators  as  an  adjunct  to  the  barometer  and  dry-bulb  ther- 
mometer in  foretelling  weather.  This  instrument  is  used  to 
measure  the  amount  of  moisture  in  the  air.  Two  equal  ther- 
mometers are  selected  and  mounted  on  the  same  frame,  the 
bulb  of  one  being  left  naked,  while  the  other  is  tied  up  in  a  thin 
muslin  covering  with  a  cotton  wick  leading  from  it  to  a  small 
cup  of  water  placed  beneath  it  and  about  three  inches  away  from 
the  wet-bulb  thermometer.  As  the  evaporation  of  the  water 
produces  cold,  the  mercury  in  the  wet-bulb  tube  will  stand  lower 
than  its  companion  the  dry  bulb,  and  the  depression  of  the  wet- 
bulb  thermometer  measures  the  humidity  of  the  atmosphere.  If 
the  water  in  the  muslin  which  covers  the  wet  bulb  be  frozen,  it 
will  not  affect  the  record,  but  will  give  the  same  reading  as 
though  frost  did  not  exist. 

In  frosty  weather,  to  insure  against  the  muslin  becoming  dry 
through  evaporation,  it  should  be  wetted  and  allowed  some  little 
time  to  freeze  before  the  reading  is  made. 

The  muslin  and  wick  should  so  act  as  to  keep  the  wet  bulb 
always  wet  so  that  evaporation  may  be  constantly  going  on  ; 
and  it  is  recommended  that  the  little  muslin  bag  and  wick  be 


THE  NAVIGATOR'S  POCKET-BOOK  69 

changed  about  once  a  month  owing  to  their  tendency  to  become 
foul  with  grit  and  smoke  and  dust. 
When  rain,  fog,  or  dew  is  promised  the  hygrometer  will  rise. 

HYFOTHENUSE.— The  longest  side  of  a  right-angle  tri- 
angle, or  the  line  opposite  the  right  angle.  (See  Base  ;  Perpen- 
dicular.) 

INCIDENCE. — In  the  artificial  horizon  the  image  of  a  body 
is  reflected  from  the  surface  of  the  quicksilver  to  the  eye,  and 
the  measured  angle  is  always  divided  by  2  in  order  to  obtain 
the  altitude.  This  proves  at  once  that  the  angle  of  incidence  is 
equal  to  the  angle  of  reflection.  The  angle  from  the  body  to  the 
quicksilver  is  the  angle  of  incidence,  and  the  angle  from  the 
quicksilver  to  the  eye  is  the  angle  of  reflection. 

INCLINATION — The  inclination  of  the  plane  of  the  earth's 
equator  to  the  plane  of  the  ecliptic  is  about  23°  28' ;  this  it  is 
that  accounts  for  the  declination  of  the  sun.  If  the  axis  of  the 
earth  was  perpendicular  to  the  plane  of  the  ecliptic,  the  sun 
would  always  be  on  the  equator,  and  in  that  case  the  corrected 
altitude  subtracted  from  90e  would  always  be  the  latitude  of  the 
observer  as  well  as  the  zenith  distance  of  the  sun. 

INDEX. — The  integer  part  of  a  logarithm.     (See  Sextant.) 

INDEX  BAR.— (See  Sextant.) 

INDEX  ERROR.— (See  Sextant.) 

INDEX  GLASS.— (See  Sextant.) 

INDUCTION.— (See  Magnetic  Induction.) 

INSTRUMENTAL  PARALLAX.— A  sextant  should  always 
be  adjusted  by  the  horizon  line  at  sea  and  by  a  distant  line  (such 
as  the  roof  of  a  remote  building)  on  shore,  because  the  horizon 
and  index  glasses  of  the  sextant  are  not  on*  the  same  horizontal 


70  THE  NAVIGATOR'S  POCKET-BOOK 

plane.  When  the  horizontal  line  of  a  near  object  is  used  the 
sextant  cannot  be  properly  adjusted  ;  but  when  the  horizontal 
line  of  a  distant  object  is  employed,  the  instrumental  error  is 
practically  eliminated. 

INTERCALARY  DAY.— A  day  that  is  inserted  in  the  cal- 
endar out  of  the  common  order  so  as  to  preserve  the  correspond- 
ence between  the  civil  and  the  solar  year.  The  29th  of  Febru- 
ary in  a  leap  year  is  an  intercalary  day. 

INTERCARDINAL  POINTS.— Northeast,  southeast,  south- 
west and  northwest  points  of  the  compass. 

INTERPOLATION.— To  alter  by  inserting  something,  as, 
for  instance,  reducing  the  given  declination  of  a  heavenly  body 
to  another  time  than  that  for  which  it  is  originally  recorded. 

INTERTROPICS.— Between  the  tropics  ;  between  the  par- 
allels  of  23i°  north  and  23i°  south. 

INVERTING  TELESCOPE.— (See  Sextant.) 

IRRADIATION. —The  apparent  enlargement  of  the  diam- 
eters of  the  sun  and  moon.  It  is  an  optical  illusion  caused  by 
the  light  of  the  object,  and  may  be  best  appreciated  in  the  illus- 
tration of  the  new  moon — the  bright  crescent  appearing  to  be  a 
part  of  a  larger  circle  than  that  of  its  shadowed  disk.  Irradia- 
tion increases  with  the  brightness  of  the  object,  and  diminishes 
in  proportion  as  the  illumination  of  the  body  and  that  of  the 
field  of  view  approach  equality,  vanishing  when  they  become 
equal.  This  apparent  augmentation  is  greatest  in  the  case  of 
the  sun  ;  but  even  in  reference  to  this  body  the  amount  of 
irradiation  seldom  exceeds  6",  so  that  for  all  practical  purposes 
the  question  need  not  be  entertained  by  the  navigator. 

KISS. — When  the  image  of  the  moon's  or  sun's  limb  is  made 


THE  NAVIGATOR'S  POCKET-BOOK  71 

to  touch  the  horizon  line  in  measuring  an  altitude,  it  is  said  to 
kiss  the  horizon. 

KNOT.— (See  Mile.) 

LANDFALL.— To  first  make  the  land,  to  obtain  the  first 
view  of  land  when  coming  from  sea.  To  make  what  is  known 
as  a  good  landfall  signifies  that  the  navigation  of  the  ship  has 
been  well  performed,  and  that  the  exact  point  of  land  discovered 
is  the  place  previously  calculated  on  by  the  navigator. 

LATITUDE. — The  distance  of  a  place  on  the  earth's  surface 
north  or  south  of  the  equator.  Latitude  is  measured  from  the 
equator  in  degrees,  minutes,  and  seconds.  In  a  degree  of  lati- 
tude there  are  sixty  geographical  or  nautical  miles  or  minutes, 
each  possessing  a  value  of  6,082.66  feet.  A  mile  of  latitude 
and  a  minute  of  latitude  mean  the  same  thing.  The  extremities 
of  the  earth's  axis,  the  north  and  south  poles,  have  a  value  of 
90°.  Latitude  may  be  said  to  be  the  angular  distance  of  a  place 
from  the  equator,  measured  on  a  meridian.  The  following  rules 
furnish  the  methods  for  finding  the  latitude  of  the  ship  by 
observations  of  the  sun,  moon,  planets,  and  stars : 

Latitude  by  the  Sun  at  Meridian. — Observe  the  altitude  (see 
Altitude)  and  note  the  Greenwich  hour  shown  by  chronometer  ; 
then  correct  the  observed  altitude  for  index  error  (if  any),  semi- 
diameter,  parallax,  dip,  and  refraction  (see  Corrected  Altitude), 
and  always  subtract  the  answer,  called  the  true  central  altitude, 
from  90°  to  obtain  the  zenith  distance,  which  name  the  opposite 
to  the  bearing  of  the  sun  at  meridian — i.e.,  north  or  south. 
Correct  the  sun's  declination  (see  Declination),  and  if  the  cor- 
rected declination  has  the  same  name  (north  or  south)  as  the 
zenith  distance,  add  the  two  quantities  ;  but  if  they  are  of 
different  names,  subtract  the  less  from  the  greater,  and  the  an- 


72  THE  NAVIGATOR'S  POCKET-BOOK 

swer  will  be  the  latitude,  which  will  take  the  name  of  the  great- 
er quantity. 

Latitude  by  the  Sun — Ex-Meridian. — It  sometimes  happens 
that  when  the  sun  has  climbed  almost  to  the  meridian  a  passing 
cloud  obscures  it  and  that  the  body  fails  to  reappear  in  time  for 
its  meridian  altitude  to  be  measured,  or,  on  the  other  hand, 
there  are  cloudy  days  when  the  sun  does  not  appear  in  the 
morning,  but  bursts  through  the  clouds,  temporarily  or  per- 
manently, some  little  time  after  meridian.  Bowditch  gives  two 
very  useful  tables  by  which  the  variation  of  the  sun's  altitude 
may  be  found  for  thirteen  minutes  of  time  on  each  side  of  the 
meridian,  which  tables  are  employed  according  to  the  following 
rule : 

Rule. — Observe  an  altitude  (see  Altitude)  and  note  the  Green- 
wich hour  shown  by  chronometer,  then  reduce  this  mean  time 
to  thp  apparent  time  at  Greenwich  by  applying  the  equation  of 
time.  Next  turn  the  ship's  longitude  into  time  and  subtract  it 
if  west  but  add  it  if  east  and  the  answer  will  be  the  apparent 
time  at  ship.  Now  with  this  time  from  ship's  noon  enter  Table 
27  and  select  the  figures  given.  Next  with  the  latitude  by 
dead-reckoning  to  the  nearest  degree  and  the  sun's  declination 
to  the  nearest  degree,  enter  Table  26  and  find  the  figures  by 
which  the  figures  taken  from  Table  27  must  be  multiplied. 
The  answer  will  represent  the  change  of  altitude  in  seconds  of 
arc  for  the  given  time  from  noon,  and  this  result  will  be  divided 
by  60  to  convert  it  into  minutes  of  arc  ;  then  this  is  always  added 
to  the  observed  altitude,  whether  the  angle  was  measured  before 
or  after  meridian,  for  in  either  case  the  sun  was  lower  than  it 
was  at  noon.  Now  correct  this  augmented  altitude  for  semi- 
diameter,  etc.,  .and  proceed  precisely  the  same  as  described  in 
the  preceding  rule  for  a  regular  meridian  sight. 


THE  XAVIGATOK'S  POCKET-BOOK  73 

Remarks. — When  the  time  from  noon  exceeds  the  limits  of 
Table  27  (13  minutes),  the  augmentation  of  the  altitude  may  be 
found  by  simply  calculating  the  square  of  the  given  number  of 
minutes,  then  multiplying  same  as  usual  by  the  figures  from 
Table  26. 

Examples.  —  If  the  time  from  noon  is  20  minutes,  take  out 
from  Table  27  the  square  for  10  minutes,  which  is  100  ;  multiply 
this  by  4  and  the  answer  will  be  400 — the  square  of  20  minutes. 
Now  multiply  this  400  by  the  quantity  given  in  Table  26  for  the 
ship's  latitude  and  the  sun's  declination,  and  the  answer  will  be 
the  required  correction  to  be  added  to  the  observed  altitude. 

If  the  time  from  noon  is  14  minutes,  take  out  the  square  of 
7  minutes,  which  is  49  ;  multiply  it  by  4,  and  the  answer  will  be 
196,  the  square  of  14  minutes,  which  will  be  multiplied  by  the 
figures  from  Table  26. 

If  the  time  from  noon  is  17  minutes,  take  out  the  square  of  8 
minutes  and  30  seconds,  which  is  72.2,  and  multiply  it  by  4, 
and  the  answer  will  be  288.8,  which  will  be  multiplied  by  the 
figures  from  Table  26. 

Explanation. — The  square  of  the  minutes  from  noon  may  also 
be  found  in  the  following  easy  manner,  independent  of  Table 
27: 

If  the  time  from  noon  is  32  minutes,  the  required  square  will 
be  found  by  multiplying  32  by  its  own  number,  hence  32  multi- 
plied by  32  equals  1,024  (32  x  32  =  1,024),  which  will  be  multi- 
plied as  usual  by  the  figures  from  Table  26. 

It  must  be  remembered  in  using  the  method  of  ex-meridian 
that  when  the  sun  passes  near  the  zenith  (that  is,  when  its  altitude 
is  high)  the  time  from  noon  at  which  the  observation  is  taken 
must  not  exceed  the  figures  in  Table  27. 

The  navigator  must  bear  in  mind  that  the  latitude  found  by  au 


74  THE  NAVIGATOK'S  -POCKET-BOOK 

ex-meridian  observation  is  the  latitude  of  the  ship  at  the  exact 
time  of  the  sight,  and  not  at  12  o'clock  (meridian).  To  carry  this 
latitude  forward  or  back  to  noon,  it  is  necessary  to  apply  to  it 
the  difference  of  latitude  selected  from  the  Table  (1  or  2)  for  the 
course  and  distance  made  by  the  ship  in  the  interval  between 
the  time  of  sight  and  noon. 

Latitude  by  the  Moon  at  Meridian — Observe  the  altitude 
(see  Altitude)  and  note  the  Greenwich  hour  shown  by  chronom- 
eter. Correct  the  latter  for  its  rate  (see  Rate),  also  the  altitude 
for  index-error  (if  any),  semi-diameter,  dip,  parallax,  and  refrac- 
tion (see  Corrected  Altitude).  Always  subtract  the  answer,  called 
the  true  central  altitude,  from  90°  to  obtain  the  zenith  distance, 
naming  the  latter  the  opposite  to  the  bearing  of  the  moon  at 
meridian— i.e.,  north  or  south.  Correct  the  moon's  declination 
(see  Declination),  and  if  the  corrected  declination  has  the  same 
name  (north  or  south)  as  the  zenith  distance,  add  the  two  quan- 
tities, but  if  they  are  of  different  names,  subtract  the  less  from 
the  greater,  and  the  answer  will  be  the  latitude,  which  will  take 
the  name  of  the  greater  quantity. 

Latitude  by  a  Planet  at  Meridian. — Observe  the  altitude 
(see  Altitude)  and  note  the  Greenwich  hour  shown  by  chronom- 
eter. Correct  the  altitude  for  index  error  (if  any),  dip,  parallax, 
and  refraction  (see  Corrected  Altitude),  and  always  subtract  the 
answer,  called  the  true  altitude,  from  90°  to  obtain  the  zenith 
distance,  naming  the  latter  the  opposite  to  the  bearing  of  the 
planet  at  meridian — i.e.,  north  or  south.  Correct  the  planet's 
declination  (see  Declination),  and  if  the  corrected  declination 
has  the  same  name  (north  and  south)  as  the  zenith  distance,  add 
the  two  quantities,  but  if  they  are  of  different  names  subtract 
the  less  from  the  greater,  and  the  answer  will  be  the  latitude, 
which  will  take  the  name  of  the  greater  quantity. 


THE  NAVIGATOR'S  POCKET-BOOK  75 

Latitude  by  a  Star  at  Meridian.— As  the  stars  are  passing 
the  meridian  at  all  hours  of  the  night,  it  becomes  a  very  simple 
problem  to  determine  the  latitude  of  the  ship  when  the  sky  is 
clear  and  when  the  horizon  is  outlined.  In  the  back  of  this 
book  will  be  found  star  tables  which  include  all  the  stars  of  the 
first  magnitude  both  in  the  northern  and  southern  hemispheres, 
and  the  navigation  stars  of  the  second  and  third  magnitudes,  to- 
gether with  the  astronomical  apparent  times  that  they  cross  the 
observer's  meridian  on  the  first  day  of  each  month  throughout 
the  year,  also  their  rough  declinations.  As  the  times  given  in 
the  tables  for  the  meridian  passages  of  the  stars  are  calcu- 
lated astronomically,  it  must  be  remembered  that  from  1  to 
12  the  hours  agree  with  P.M.  civil  apparent  time,  but  13  hours 
means  1  o'clock  in  the  morning,  14  hours  means  2  A.M.,  20 
hours  means  8  A.M.,  etc.  The  declinations  of  the  stars  are 
practically  constant,  and  do  not  require  correction,  but  the 
small  annual  changes  of  declination  are  shown  in  the  al- 
manac. 

The  stars  come  to  the  meridian  four  minutes  earlier  on  each 
successive  day,  therefore  to  find  the  time  of  a  star's  meridian 
passage  for  any  day  between  the  first  and  last  of  the  month, 
multiply  by  4  the  number  of  days  that  have  passed  since  the 
first  of  the  month  and  always  subtract  this  sum  from  the  time 
of  the  meridian  passage  given  for  the  first.  For  example  sup- 
pose that  it  was  required  to  know  the  time  of  the  meridian  pas- 
sage of  the  star  Sirius  on  the  10th  of  January.  The  differ- 
ence between  1  and  10  is  9,  so  we  multiply  the  latter  by  4,  and 
receive  36  for  an  answer,  and  this  we  subtract  from  the  time 
given  for  the  star's  meridian  passage  on  the  1st  of  January  (11  h. 
50  m.)  and  obtain  11  h.  14  m.,  which  represents  the  time  that 
Sirius  will  cross  the  meridian  of  the  ship  on  the  10th  day  of 


76  THE  NAVIGATOR'S  POCKET-BOOK 

January.  Proceed  to  find  the  latitude  in  the  following  man 
ner : 

Rule. — Observe  the  altitude  (see  Altitude)  and  correct  same 
for  index  error  (if  any),  dip,  and  refraction  (see  Corrected  Alti- 
tude), then  always  subtract  the  answer,  called  the  true  altitude, 
from  90°  to  obtain  the  zenith  distance,  and  name  the  latter  the 
opposite  to  the  bearing  of  the  star  at  meridian — i.e.,  north  or 
south.  Now  set  the  star's  declination  (given  in  the  almanac) 
under  the  zenith  distance,  and  if  they  are  of  the  same  name  (north 
or  south)  add  the  two  quantities,  but  if  they  are  of  different 
names,  subtract  the  less  from  the  greater,  and  the  answer  will  be 
the  latitude,  which  will  take  the  name  of  the  greater  quantity. 

Remarks. — This  star  method  is  the  shortest  and  simplest  of 
all  latitude  calculations. 

Whenever  it  is  possible  the  navigator  should  observe  stars  both 
north  and  south  of  him  (north  and  south  of  his  zenith),  then  take 
the  mean  of  the  two  latitudes  obtained,  as  this  will  eliminate  or 
halve  possible  errors  in  the  way  of  misjudging  the  horizon,  etc. 

Should  the  navigator  require  the  time  of  the  meridian  passage 
of  a  star  not  contained  in  either  of  the  star  tables  in  this  book, 
he  may  calculate  it  readily  by  the  following  method  : 

First,  select  the  star's  right  ascension  for  the  given  day  from 
the  star  page  in  the  back  of  the  Nautical  Almanac,  also  the  sun's 
right  ascension  from  the  almanac  for  the  given  day  of  the 
month. 

Second,  if  the  star's  right  ascension  is  less  than  the  sun's  right 
ascension  add  twenty-four  hours  to  the  former,  but  if  not  then 
let  it  stand  as  selected.  Now  subtract  the  sun's  right  ascension 
from  the  star's  right  ascension,  and  the  answer  will  be  th^  astro- 
nomical apparent  time  of  the  star's  meridian  passage. 

Latitude   by  the  Pole  Star  at  Any  Hour. — The  following 


THE  NAVIGATOR'S  POCKET-BOOK  77 

rule  for  finding  the  latitude  at  any  hour  of  the  night  by  the  Pole 
Star  when  it  is  out  of  the  meridian  is,  to  a  certain  extent,  unsat- 
isfactory, inasmuch  as  it  cannot  be  depended  upon  to  give  the 
ship's  position  within  two  or  three  miles,  although  oftentimes 
with  a  good  horizon  the  results  are  quite  correct. 

Rule. — Observe  an  altitude  (see  Altitude)  at  any  hour  when 
the  star  can  be  seen,  and  correct  the  altitude  for  index  error  (if 
any),  dip,  and  refraction  (see  Corrected  Altitude) ;  the  answer 
will  be  the  true  altitude.  To  the  time  shown  by  the  ship's 
clock  when  the  observation  was  taken  add  four  minutes  for 
every  degree  of  longitude  sailed  east  since  the  clock  was  last 
set,  but  subtract  four  minutes  for  every  degree  sailed  west. 
Turn  this  corrected  local  apparent  time  into  astronomical  time 
by  simply  counting  the  hours  from  noon  to  noon  in  numerical 
order  (1  to  24),  instead  of  dividing  them  into  A.M.  and  P.M.  (see 
Astronomical  Time).  To  the  astronomical  time  at  the  ship  al- 
ways add  the  sun's  right  ascension  from  the  Nautical  Almanac 
for  the  given  day,  and  if  the  result  exceeds  twenty-four  hours 
then  subtract  twenty-four  hours  and  apply  the  remainder  (which 
is  called  the  right  ascension  of  the  meridian)  in  the  Pole  Star 
table  in  the  back  of  this  book,  and  opposite  the  hours  and  min- 
utes will  be  found  a  correction  which  will  either  be  added  to  or 
subtracted  from  the  true  altitude,  according  to  the  given  sign  ; 
if  +  add,  if  —  subtract.  The  answer  will  be  the  latitude,  al- 
ways north,  as  the  star  cannot  be  seen  south  of  the  equator. 

Latitude  by  a  Meridian  Altitude  Below  the  Pole. — In 
high  latitudes  when  observing  a  meridian  altitude  of  a  body  be- 
low the  pole  the  altitude  will  grow  less  and  less  until  the  lowest 
part  of  the  circle  is  reached,  at  which  point  the  body  will  cross 
the  meridian  below  the  pole,  after  which  it  will  commence  to 
rise. 


78  THE  NAVIGATOR'S  POCKET-BOOK 

To  find  the  latitude  by  a  body  when  it  crosses  the  meridian 
below  the  pole,  correct  the  altitude  as  usual,  then  obtain  the 
polar  distance  by  subtracting  the  body's  corrected  declination 
from  90°.  Now  add  together  the  polar  distance  and  the  true 
altitude,  and  the  result  will  be  the  latitude. 

Latitude  by  Dead-Reckoning.— (See  Dead-Reckoning.) 
Latitude  by  the  Artificial  Horizon.— (See  Artificial  Horizon.) 
LAW  OF  STORMS.— When  a  regular  wind  is  so  obstructed 
as  to  produce  a  hurricane  the  wind  assumes  a  rotary  motion  and 
extends  over  an  area  of  from  thirty  to  several  hundreds  of  miles 
in  diameter,  revolving  with  greatest  velocity  near  the  vortex. 
The  centre,  however,  of  a  hurricane  is  a  space  of  calm  in  which 
frightful  and  confused  seas  are  to  be  experienced.  In  the 
northern  hemisphere  these  winds  revolve  contrary  to  the  move- 
ments of  the  hands  of  a  clock,  and  in  the  southern  hemisphere 
they  revolve  in  the  same  direction  as  the  hands  of  a  clock.  The 
course  or  track  followed  by  a  hurricane  is  tolerably  definite,  as 
will  be  seen  by  the  following : 

Track  in  the  Northern  Hemisphere.— The  cyclone  has  its 
origin  between  the  parallels  of  10°  and  18°  north,  and  advances, 
or  rolls  forward,  in  a  general  northwesterly  direction.  Be- 
tween the  parallels  of  25°  and  30°  it  recurves  and  advances  in  a 
general  northeasterly  direction.  From  the  start  and  until  it  breaks 
up  the  hurricane  spreads  out,  or  increases  its  diameter,  while 
the  wind,  to  some  extent,  decreases  as  the  area  of  the  storm 
widens.  West  India  hurricanes,  as  a  rule,  range  between  the 
parallels  of  10°  and  50°  north  and  the  meridians  of  55°  and  85° 
west,  their  average  rate  of  progression  being  three  hundred 
miles  a  day. 

Track  in  the  Southern  Hemisphere. — The  cyclone  has  its 
origin  in  the  equatorial  regions  (rarely  within  6°  of  the  equator) 


THE  NAVIGATOR'S  POCKET-BOOK 


79 


and  advances,  or  rolls  forward,  in  a  general  southwesterly  direc- 
tion, and  somewhere  about  the  parallel  of  25°  south  it  recurves 
and  advances  in  a  general  southeasterly  direction,  increasing 
in  diameter  from  the  start,  and  finally  breaks  up. 

Barometer  and  Weather  Indications.— The  barometer  often 
rises  suddenly  just  in  front  of  a  storm,  owing  to  the  air  bank- 
ing up  there ;  consequently  if  the  general  appearance  of  the 
weather  indicates  a  storm  the  rise  of  the  barometer  is  not  to 
be  accepted  as  evidence  that  a  storm  will  not  be  experienced, 
but  rather  that  one  is  at  hand.  The  approach  of  a  cyclone 
may  often  be  foretold  by  a  greenish-tinted  sky,  a  blood-red 
or  bright  yellow  sunset,  a  heavy,  unaccountable  wave-swell, 
or  a  thick,  lurid  appearance  of  the  atmosphere.  A  restless  state 
of  the  barometer  is  another  warning.  After  the  ship  has  entered 
the  storm  disk,  if  a  rapid  fall  of  the  barometer  is  experienced  it 
may  be  accepted  as  evidence  of  a  violent  storm  of  small  diam- 
eter ;  but  if  a  gradual  fall  of  the  barometer  is  noted,  then  the 
opposite  conditions  may  be  counted  on. 

Distance  of  the  Storm  Centre. — The  following  table  is  given 
to  show  the  approximate  distance  that  has  been  calculated  for 
the  centre  of  the  cyclone,  according  to  the  average  fall  of  the 
barometer  per  hour.  It  is  a  rough  calculation,  but  it  has  a 
certain  value  : 


Average  Pall  of  Barometer  per  Hour. 

Distance  in  Miles  from  Storm  Centre. 

From  0.02  in.  to  0.06  in. 
"      0.06      "     0.08  " 
"      0.08      "    0.12  " 
"      0.12      "    0.15  " 

From  250  to  150. 
"      150  '•  100. 

"     100  "     80. 
"       80  "•   50. 

80  THE  NAVIGATOR'S  POCKET-BOOK 

Practical  Oonsiderations. — The  revolving-storm  problem, 
when  considered  practically  as  regards  the  safe  navigation  of 
the  ship,  is  simple.  First,  locate  the  centre  of  the  cyclone ; 
second,  ascertain  the  semicircle  in  which  the  ship  is ;  third, 
determine  the  direction  in  which  the  storm  is  moving,  and 
decide  upon  what  course  to  pursue. 

Bearing  of  the  Storm  Centre. — Face  the  wind  and  note  its 
bearing  by  compass,  then,  in  north  latitudes,  count  eight  points 
(90°)  to  the  right ;  but  in  south  latitudes  count  eight  points  to  the 
left  of  the  wind's  eye.  If  the  navigator  in  the  northern  hemi- 
sphere has  the  wind  at  east,  the  centre  of  the  cyclone  will  bear 
south  of  him.  If  a  navigator  in  the  southern  hemisphere  has 
the  wind  at  east,  the  centre  of  the  cyclone  will  bear  north  of 
him. 

Semicircles  of  Storm-Disk. — The  storm-disk  being  divided 
into  two  equal  parts  by  the  line  or  axis  of  the  storm  track,  these 
two  semicircles  are  named  according  to  the  following :  Look 
in  the  direction  toward  which  the  storm  is  moving,  then  the 
portion  that  lies  on  the  right  side  of  this  line  is  known  as  the 
right  semicircle,  and  the  portion  that  lies  on  the  left  side  is  known 
as  the  left  semicircle.  In  the  right  semicircle  the  wind  changes  to 
the  right— from  north  toward  east,  from  east  toward  south,  from 
south  toward  west,  and  from  west  toward  north  ;  but  in  the  left 
semicircle  the  wind  changes  to  the  left — from  north  toward 
west,  from  west  toward  south,  from  south  toward  east,  and 
from  east  toward  north.  The  first  change  of  wind  will  prove 
to  the  navigator  the  semicircle  he  is  in. 

To  Avoid  the  Centre. — In  the  northern  hemisphere,  if  the 
ship  is  in  the  right  semicircle,  haul  by  the  wind  on  the  star- 
board tack  and  keep  going  as  long  as  possible  ;  but  if  the  ship  is 
in  the  left  semicircle,  bring  the  wind  on  the  starboard  quarter, 


THE  NAVIGATOR'S  POCKET-BOOK  81 

note  the  compass  course  when  the  ship  is  so  headed,  and  keep  to 
that  course.  In  the  southern  hemisphere,  if  the  ship  is  in  the 
right  semicircle,  bring  the  wind  on  the  port  quarter,  note  the 
direction  of  the  ship's  head  by  compass,  and  keep  to  that  course  ; 
but  if  the  ship  is  in  the  left  semicircle,  haul  by  the  wind  on  the 
port  tack,  and  keep  going  as  long  as  possible. 

Tack  to  Heave-to  On. — If  obliged  to  heave-to,  act  accord- 
ing to  the  following  simple  rule :  If  in  the  right  semicircle, 
heave-to  on  the  starboard  tack  ;  but  if  in  the  left  semicircle, 
heave-to  on  the  port  tack.  This  rule  applies  to  all  parts  of  the 
world,  and  should  be  impressed  upon  the  navigator's  mem- 
ory. 

On  the  Storm-Track. — When  the  ship  is  on  the  storm  track 
in  front  of  the  centre,  she  will  not  experience  a  change  of  wind, 
but  will  have  a  falling  barometer  and  constantly  increasing  se- 
verity of  weather  ;  but  if  in  the  rear  of  the  storm-centre,  she  will 
have  a  rising  barometer  and  a  gradual  moderation  of  the  weath- 
er. In  the  northern  hemisphere,  if  in  front  of  the  centre,  put 
the  ship  before  the  wind,  note  the  compass  course  when  the 
ship  is  so  headed,  and  keep  to  that  course,  and  if  obliged  to 
heave-to  do  so  on  the  port  tack,  but  if  in  the  rear  of  the  centre, 
run  out  with  the  wind  on  the  starboard  quarter,  or  heave-to  on 
the  starboard  tack.  In  the  southern  hemisphere,  if  in  front 
of  the  centre,  put  the  ship  before  the  wind,  note  the  com- 
pass course  when  the  ship  is  so  headed  and  keep  to  that  course, 
and  if  obliged  to  heave-to  do  so  on  the  starboard  tack  ;  but  if  in 
the  rear  of  the  centre,  run  out  with  the  wind  on  the  port  quar- 
ter, or  heave-to  on  the  port  tack. 

Remarks. — When,  according  to  the  foregoing  rules,  a  ship  is 
laid-to  on  the  port  tack  in  the  left  semicircle  in  the  northern 
hemisphere,  and  on  the  starboard  tack  in  the  right  semicircle  in 
6 


82  THE  NAVIGATOR'S  POCKET-BOOK 

the  southern  hemisphere,  her  head  will  be  directed  toward  the 
storm  centre.  There  will  be  no  danger  in  this,  however,  as  the 
ship  will  not  head-reach  to  any  extent,  consequently  she  will 
not  approach  the  storm  centre  sufficient  to  amount  to  anything. 
Laid*to  in  this  way,  she  will  come  up  and  bow  the  sea  as  the 
wind  shifts,  whereas  if  she  was  laid-to  on  the  opposite  tack  she 
would  be  headed  off  with  every  shift  of  wind,  and  would  ulti- 
mately bring  the  sea  on  the  beam  and  quarter,  and  would  prob- 
ably founder. 

It  has  been  computed  that  West  Indian  cyclones,  commencing 
with  a  very  small  diameter,  increase  the  same  to  six  hundred  and 
one  thousand  miles  before  breaking  up.  In  the  Indian  Ocean 
they  spread  out  from  one  hundred  to  six  hundred  miles,  and  in 
the  China  Sea  from  eighty  to  four  hundred  miles. 

The  progressive  rate  of  the  West  Indian  hurricane  or  cyclone 
is  about  three  hundred  miles  a  day,  and  the  rate  of  the  Bay  of 
Bengal  and  China  Sea  cyclones,  two  hundred  miles  a  day  ;  but 
the  rate  of  the  Indian  Ocean  cyclone  varies  from  fifty  to  two 
hundred  miles  a  day. 

The  cyclone  season  for  the  West  Indies,  Atlantic  Coast  of 
America,  and  the  coasts  of  Mexico  and  Lower  California  is  from 
July  to  October.  The  cyclone  season  for  the  Malabar  Coast  and 
Bay  of  Bengal  embraces  the  five  months  of  April  and  May, 
October,  November,  and  December.  The  cyclone  season  for  the 
China  Sea  extends  from  July  to  November.  The  cyclone  sea- 
son on  the  coast  of  Japan  takes  in  August,  September,  and 
October. 

LEEWAY. — The  sideways  drift  of  a  vessel  through  the 
water  owing  to  the  pressure  of  the  wind  on  her  spars,  sails,  and 
side.  Running  free,  a  vessel  makes  no  leeway,  as  all  the  wind 
and  wave  force  exerted  is  on  the  line  of  her  course ;  but  the 


THE  NAVIGATOR'S  POCKET-BOOK  83 

closer  the  ship  is  hauled  to  the  wind  the  more  she  will  be  forced 
to  leeward.  When  a  steam  vessel  makes  leeway  owing  to  a  heavy 
beam  wind  and  sea,  it  is  recorded  in  the  log-book  under  the  head 
of  "  Send  of  the  Sea."  The  manner  of  determining  the  amount 
of  leeway  being  made  by  a  vessel  is  extremely  simple :  It  is 
only  necessary  to  note  the  line  of  the  keel  by  observing  the 
course  of  the  ship,  then  to  see  what  angle  the  wake  makes  with 
this,  and  that  will  give  at  once  the  amount  of  leeway  being 
made. 

Example.— A.  vessel,  we  will  say,  is  heading  east  on  the  star- 
board tack ;  the  heel  of  her  keel  is  west ;  the  wake  bears  by 
compass  west-by-south,  consequently  the  wake  makes  an  angle 
of  one  point  with  the  line  of  the  keel,  which  amount  (one  point) 
is  the  leeway  being  made.  Under  these  circumstances  the  ship 
is  really  making  an  east-by-north  course. 

Remarks. — If  a  patent  log  is  being  towed,  the  angle  made 
by  the  line  as  compared  with  the  keel  will  give  the  amount  of 
leeway. 

Some  vessels  have  a  graduated  half -circle  of  brass  tacked  on 
the  middle  of  the  taffrail,  and  when  desiring  to  ascertain  the 
amount  of  leeway,  either  by  day  or  night,  the  bight  of  the  log- 
line  is  carried  to  this  half-circle  and  held  in  the  rear  centre,  then 
the  angle  made  by  the  line  with  the  zero  point  of  the  circle  will 
give  the  answer  either  in  degrees  or  quarter  points  of  the  com- 
pass according  as  the  circle  is  graduated. 

In  case  the  vessel  is  not  towing  a  log,  the  hand-lead  may  be 
temporarily  thrown  overboard  and  allowed  to  trail  astern,  and 
the  angle  measured  by  it,  as  already  explained. 

When  the  vessel  is  making  no  leeway,  the  wake  will  be  left 
dead  astern,  but  if  leeway  is  being  made,  the  wake  will  trend 
away  on  the  weather  quarter.  (See  Corrected  Course.) 


84  THE   KAVIGATOB^S   POCKET-BOOK 

LEAGUE. — A  league  is  generally  conceded  to  have  a  value 
of  three  nautical  miles,  but  it  varies  in  different  countries.  In 
the  United  States,  France,  Italy,  and  England,  a  league  contains 
6,075  yards;  Spain,  7,416  yards  ;  Holland  and  Germany,  8,100 
yards  ;  Russia,  8,468  yards. 

LENS. — A  piece  of  glass  formed  so  as  to  change  the  direction 
of  rays  of  light  when  passing  through  it,  as  the  magnifying 
glasses  used  in  telescopes. 

LIMB (See  Upper  Limb.) 

LINE. — A  name  for  the  equator. 

LINE  OF  COLLIMATION.— Same  as  axis  of  collimation. 

LINE   OF  NO  VARIATION.— (See  Compass.) 

LIQUID  COMPASS. — A  compass  card  enclosed  and  entirely 
submerged  in  a  chamber  of  alcohol  and  water  or  refined  petro- 
leum, to  give  steadiness  to  the  card  and  to  prevent  it  from  flying 
about  in  a  manner  peculiar  to  a  dry-card  compass  when  sailing 
in  rough  water. 

LOCAL  ATTRACTION.— (See  Compass.) 

LOCAL  APPARENT  TIME. — Time  calculated  by  the  pas- 
sage of  the  sun  over  the  observer's  meridian.  The  length  of  a 
solar  day  varies  according  to  the  sun's  movement.  (See  Noon.) 

LOCAL  MEAN  TIME. — Time  calculated  by  the  imaginary 
passage  of  an  imaginary  sun  over  the  observer's  meridian. 
This  is  known  as  the  mean  sun,  and  is  adopted  so  as  to  give  the 
civil  day  a  value  of  exactly  twenty -four  hours.  (See  Mean  Sun.) 

LOCAL  TRANSIT. — The  passage  of  a  heavenly  body  over 
the  meridian  of  the  observer. 

LOG. — To  make  a  memorandum  of  anything  in  the  log-book 
is  to  "  log  "  it.  (See  Chip  Log  ;  Log-Book  ;  Patent  Log.) 


THE  NAVIGATOR'S  POCKET-BOOK  85 

LOGARITHM. — A  logarithm  may  be  defined  as  the  expo- 
nent of  the  power  to  which  a  given  number,  known  as  a  base, 
must  be  raised  in  order  to  produce  a  certain  number.  By  the 
employment  of  logarithms  difficult  and  tedious  problems  in 
navigation  are  so  simplified  as  to  be  calculated  by  men  whose 
knowledge  of  arithmetic  does  not  extend  beyond  the  four  com- 
mon rules  of  addition,  subtraction,  multiplication,  and  division. 
(Table  44.) 

To  Select  Logarithms  for  Degrees  and  Minutes. — The  giv- 
en number  of  degrees  will  be  found  at  the  bottom  of  the  page 
when  between  45°  and  135°,  otherwise  at  the  top.  The  minutes 
of  the  angle  must  be  found  in  that  column  marked  M,  which 
stands  on  the  side  of  the  page  on  which  the  degrees  were  found. 
If  the  degrees  are  found  at  the  top  of  page,  the  sine,  cosine,  etc. , 
must  be  read  from  the  top,  but  if  the  degrees  are  found  at  the 
bottom  of  page,  then  the  sine,  cosine,  etc.,  must  be  read  from 
the  bottom.  Opposite  the  given  number  of  minutes  will  be 
found  the  required  logarithm. 

To  Select  Proportions  for  Seconds. — The  proportional  parts 
will  be  found  by  the  columns  of  differences  for  seconds.  The 
correction  of  the  logarithm  for  any  number  of  seconds  is  found 
by  entering  the  left-hand  column  of  the  table  markedM'at  the 
top,  and  finding  the  number  of  seconds  in  the  regular  minute 
column,  and  opposite  to  this  in  the  column  of  differences  will 
be  found  the  corresponding  correction.  Thus  on  the  page  which 
contains  the  log.  sines,  tangents,  etc.,  for  30°,  the  corrections  for 
25"  are  9  for  the  columns  A.  A. ;  12  for  the  columns  B.B. ,  and  3 
for  the  columns  C.C. ;  so  that  if  it  were  required  to  find  the 
sine,  tangent,  or  secant  of  30°  12'  25"  we  would  add  these  cor- 
rections respectively  to  the  logarithms  corresponding  to  30°  12', 
because  these  logarithms  increase  in  proceeding  from  30°  12'  to 


86  THE  NAVIGATOR'S  POCKET-BOOK 

30°  13'.  If  the  logarithms  decreased  from  30°  12'  to  30e  13',  we 
would  subtract  this  correction. 

To  Correct  Time  for  Proportions  of  Logarithms. — In  work- 
ing a  chronometer  sight,  when  selecting  the  time  for  the  logarithm 
called  "sine  of  apparent  time  at  ship,"  if  it  is  impossible  to  match 
the  logarithm  in  the  column  of  sine,  take  the  nearest  logarithm  to 
it,  calculate  the  difference  between  the  two  by  simple  subtraction, 
and  note  the  alphabetical  sign  (A.B.  or  C.)  belonging  to  the  col- 
umn  ;  then  apply  this  difference  in  the  little  table  of  correction  at 
the  foot  of  page,  opposite  the  proper  letter,  and  find  the  correction 
overhead  given  in  seconds  to  be  added  to  or  subtracted  from  the 
time  corresponding  to  the  sine  accepted.  This  is  done  in  order 
to  obtain  the  full  value  of  time  for  the  logarithm  "  sine  of  appar- 
ent time  at  ship."  For  example  :  Should  we  require  the  P.M. 
time  for  the  log.  sine  of  9.70167,  we  would  select  the  nearest  log. 
to  this,  which  is  9.70159,  and  find  by  subtraction  that  the  differ- 
ence is  8.  Now  the  P.M.  time  corresponding  to  9.70159  is  4  h.  01 
m.  36  sec. ,  which  we  note.  We  now  apply  the  8  in  the  foot  table 
opposite  the  letter  A,  and  find  a  correction  of  three  seconds  over- 
head, which,  in  this  case,  we  add  to  the  time  selected,  making 
the  same  4  h.  01  m.  39  sec.  This  correction  is  added  because  in 
this  instance  the  time  increases  as  the  logarithms  increase,  and 
having  taken  out  the  time  for  an  inferior  log.  we  must  add  the 
correction  to  obtain  the  full  measure  of  time  for  the  proper  log. 

To  Convert  Logarithms  into  Degrees.  —  Select  from  the 
table  the  degrees  and  minutes  for  the  next  smallest  logarithm  to 
the  one  given,  then  ascertain  by  subtraction  the  difference  be- 
tween them,  and  with  this  difference  apply  it  on  the  same  page 
in  the  proper  "  Dif."  column,  and  opposite  in  the  M.  column  to 
the  left  will  be  given  the  number  of  seconds  required  to  complete 
the  degrees,  minutes,  and  seconds. 


THE  NAVIGATOR'S  POCKET-BOOK  87 

LOG-BOOK. — The  log-book  is  a  journal  of  all  that  transpires 
of  importance  on  board  ship.  Log-books  in  general  use  may  be 
described  as  follows : 

Over  the  first  column  is  marked  the  letter  H.,  standing  for 
the  hours  of  the  day  and  night,  the  figures  below  it  running 
consecutively  from  midnight  to  noon  (1  to  12)  and  then  from 
noon  to  midnight  (1  to  12),  making  the  same  divisions  of  the 
twenty-four  hours  as  are  used  on  shore.  The  log-book  is  kept 
in  civil  time  now  instead  of  the  old  method  of  sea  time,  as  ex- 
plained under  the  head  of  Sea  Day. 

Over  the  next  column  will  be  seen  the  letter  K.,  standing  for 
miles,  or  as  they  are  nautically  called,  "  knots." 

Next  will  be  seen  the  letter  F.,  meaning  furlongs,  a  furlong 
standing  for  one-eighth  of  a  knot.  If  the  ship  had  sailed  during 
the  watch  forty  miles  and  a  half,  the  half  knot  would  be  entered 
as  four  furlongs.  Furlongs  are  divided  by  8  to  convert  them 
into  miles. 

Following  along  to  the  right  we  next  find  the  word  Courses, 
under  which  heading,  and  against  the  hour,  will  be  noted  the 
course  of  the  ship  by  the  steering  compass.  Every  time  the 
course  is  changed,  the  log  must  be  noted,  and  this  reading  and 
the  time  recorded  in  the  log-book  under  the  proper  headings. 

Next  is  the  column  of  Leeway.  In  this  column  is  entered  the 
amount  of  leeway  for  the  respective  courses  sailed,  determined 
by  the  officer  of  the  watch. 

The  two  following  columns  are  for  the  standing  of  the  Ther- 
mometer and  Barometer. 

The  last  column  is  headed  Remarks,  and  under  this  head  will 
be  recorded  all  matters  of  importance  occurring  on  board,  such 
as  carrying  away  sails  and  spars,  accidents  to  crew,  work  pro- 
gressing, also  meeting  with  vessels,  state  of  the  weather,  etc. 


88  THE  NAVIGATOR'S  POCKET-BOOK 

Half  way  between  midnight  and  midnight  (top  and  bottom  of 
the  page)  will  be  seen  the  following  headings  contained  in  red 
rulings  :  Course,  Distance,  Diff.  of  Lat.,  Departure,  Lat.  by 
D.  R.,  Lat.  by  Obs.,  Variation,  Diff.  of  Long.,  Long,  by  D.R., 
Long  by  Obs.  We  will  take  them  up  in  their  order  in  dealing 
with  them : 

Course. — The  bearing  of  the  ship  from  her  former  calculated 
position  is  entered  under  this  head.  This  is  fully  explained 
under  the  head  of  Dead-Reckoning. 

Distance. — On  the  line  of  bearing  of  the  ship  from  the 
former  position  the  distance  is  measured  in  a  straight  line,  and 
set  down. 

Diff.  of  Lat. — Here  is  entered  the  amount  of  latitude  between 
the  position  last  calculated  and  the  position  arrived  at  accord- 
ing to  dead-reckoning. 

Departure. — In  this  space  is  entered  the  number  of  departure 
miles  (knots)  the  ship  is  either  east  or  west  of  her  place  last 
calculated. 

Lat.  by  D.  R. — By  applying  the  difference  of  latitude  made 
to  the  latitude  of  the  ship  last  determined,  we  obtain  the  lati- 
tude by  dead-reckoning,  the  same  being  marked  under  this 
heading. 

Lat.  by  Obs. — This  is  calculated  at  noon  by  the  sextant,  and 
the  result  placed  in  this  space. 

Variation.— The  variations  of  the  compass  on  the  different 
courses  are  shown  under  this  heading. 

Diff.  of  Long. — The  number  of  minutes  of  longitude  made 
(estimated  by  using  the  middle-latitude  as  a  course  in  Table  2, 
and  applying  the  whole  departure)  are  shown  under  this  head. 

Long,  by  D.R. — The  longitude  by  dead-reckoning  is  found 
by  applying  the  difference  of  longitude  made  to  the  longitude 


THE  NAVIGATOR'S  POCKET-BOOK  89 

of  the  ship  last  determined,  and  the  same  is  recorded  under  this 
head. 

Long,  by  Obs. — The  longitude  by  observation  at  noon  (me- 
ridian) may  be  calculated  by  equal  altitudes,  but,  as  a  rule,  the 
morning  position  is  carried  forward  to  noon  and  the  afternoon 
position  is  carried  back  to  noon,  in  the  way  explained  following  : 

To  Carry  Longitude  Forward. — Suppose  that  we  should  ob- 
tain a  chronometer  sight  at  8  o'clock  in  the  morning  and 
determine  our  longitude  at  that  time.  Between  the  time  of  this 
sight  and  noon  four  hours  elapse,  and  in  order  to  find  our  lon- 
gitude at  noon  all  that  it  is  necessary  to  do  is  to  correct  the 
course  or  courses  sailed  since  8  A.M.  ;  select  the  departure  from 
Table  2,  turn  it  into  minutes  of  longitude  for  the  parallel  of  the 
ship,  and  apply  this  difference  of  longitude  to  the  longitude  of 
the  ship  found  at  8  o'clock.  Of  course  this  will  not  be  exactly 
the  longitude  by  observation,  but  it  will  be  so  near  the  truth 
that  for  practical  purposes  it  may  be  considered  as  the  ship's 
longitude  by  observation  at  noon. 

To  Carry  Longitude  Back. — Suppose  that  no  observation 
was  secured  during  the  morning,  but  that  a  sight  was  obtained 
at  4  o'clock  in  the  afternoon.  In  order  to  carry  the  longitude 
back  to  noon  so  as  to  enter  it  in  its  column,  we  must  find  the 
difference  of  longitude  made  by  the  ship  since  noon,  and  apply 
it  to  the  longitude  of  the  ship  found  at  4  P.M. 

Symbols. — Letters  and  numbers  are  sometimes  employed  in 
log-books  to  represent  the  weather,  wind,  and  sea.  The  follow 
iug  shows  the  various  notations  : 

Weather  is  indicated  by  the  small  italic  letters  :  b  (blue  sky), 
c  (detached  clouds),  d  (drizzling  rain),  /  (foggy),  g  (gloomy),  h 
(hail),  I  (lightning),  m  (misty),  o  (overcast),  p  (passing  showers), 
q  (squally),  r  (rainy),  s  (snow),  t  (thunder),  u  (ugly,  threatening), 


90  THE  NAVIGATOR'S  ^POCKET-BOOK 

v  (visibility,  clearness),  w  (wet,  dew).  When  a  bar  ( — )  is  placed 
under  a  letter  it  augments  its  signification,  and  when  a  bar  and  a 
dot  (—)  are  placed  under  it,  it  signifies  heavy  and  continuous 
weather  of  the  character  indicated. 

Wind  is  denoted  by  the  numerals,  0  (calm),  1  (light  air),  2 
(light  breeze),  3  (gentle  breeze),  4  (moderate  breeze),  5  (fresh 
breeze),  6  (strong  breeze),  7  (moderate  gale),  8  (fresh  gale),  9 
(strong  gale),  10  (whole  gale),  11  (storm),  12  (hurricane). 

Sea  swell  is  indicated  by  the  capital  letters,  S  (smooth),  M 
(moderate),  L  (long),  R  (rough),  C  (cross),  H  (heavy),  V  H  (very 
heavy). 

Remarks. — Steamship  log-books  are  ruled  slightly  different 
from  those  of  sailing  ships,  as  there  is  no  column  heading  for 
leeway  ;  but  instead  there  are  columns  for  slip  of  wheel,  etc. 
(See  Current  Sailing  ;  Departure  ;  Drift ;  Heave  of  the  Sea  ; 
Slip  of  Wheel.) 

Watches. — The  seven  watches  of  the  log-book  are  named  as 
follows : 

From  8  P.M.  to  12  midnight,  the  First  Watch. 

From  midnight  to  4  A.M.,  the  Mid  Watch. 

From  4  A.M.  to  8  A.M.,  the  Morning  Watch 

From  8  A.  M.  to  noon,  the  Forenoon  Watch. 

From  noon  to  4  P.M,  the  Afternoon  Watch. 

From  4  P.M.  to  6  P.M.,  the  First  Dog  Watch. 

From  6  P.M.  to  8  P.M.,  the  Second  Dog  Watch. 

The  reason  for  the  watch  from  8  P.M.  to  midnight  being  called 
the  First  Watch,  is  because  when  a  ship  puts  to  sea  the  first 
watch  is  always  set  at  8  P.M.  The  captain  always  stands  the 
first  watch  out,  and  the  mate  stands  the  first  watch  coming  home. 
The  captain's  watch  is  called  the  starboard,  and  the  mate's  the 
port  watch. 


THE  NAVIGATOR'S  POCKET-BOOK  91 

Note. — Never  ditto  figures  in  the  log-book,  but  where  the 
same  course  and  wind  are  continuous,  always  employ  ditto 
marks,  as  it  will  keep  the  log-page  neater,  and  make  it  easier  to 
read. 

LOG-SLATE.-— The  deck  slate  on  which  the  officer  of  the 
watch  keeps  a  record  of  the  ship's  speed,  course,  etc.,  and  from 
which  the  smooth  log-book  is  made  up.  To  enter  anything  on 
the  slate  is  to  "  log  "  it. 

LONGITUDE. — The  distance  of  a  place  on  the  earth's  sur- 
face east  or  west  of  some  given  prime  meridian.  Longitude 
is  measured  in  degrees,  minutes,  and  seconds,  counting  as  high 
as  180°  east  and  180°  west,  thus  completing  the  circumference  of 
the  globe.  The  meridian  of  180°  east  and  the  meridian  of  180° 
west  are  represented  by  the  same  line,  so  that  a  vessel  may  be 
on  both  at  the  same  time.  Longitude  may  be  defined  as  the 
angle  at  the  pole  contained  between  two  meridians,  one  passing 
through  the  place  in  question  and  the  other  through  some  con- 
ventional point  from  which  longitudes  are  reckoned.  (See 
Prime  Meridian.)  The  following  rules  furnish  the  methods  for 
finding  the  longitude  of  the  ship  by  observations  of  the  sun, 
moon,  planets,  and  stars. 

Longitude  by  Equal  Altitudes  of  the  Sun.  —  Observe  an 
A.M.  altitude  (see  Altitude)  and  at  the  instant  of  contact  note  the 
hour,  minute,  and  second  shown  by  chronometer.  When  the 
sun  falls  to  the  same  altitude  after  noon,  note  again  the  chronom- 
eter. Add  these  two  times  together  and  divide  by  2,  then  apply 
the  rate  correction,  and  the  answer  will  show  the  mean  time 
that  it  was  at  Greenwich  when  it  was  apparent  noon  at  ship.  Re- 
duce this  Greenwich  mean  time  to  apparent  time  by  applying  to 
it  the  corrected  equation  of  time  (see  Equation  of  Time),  and  if 


92  THE  NAVIGATOR'S  ^POCKET-BOOK 

the  ship  is  in  west  longitude  simply  turn  this  apparent  time  into 
degrees  (Table  7),  and  the  answer  will  be  the  longitude  of  the 
ship ;  but  if  the  vessel  is  in  east  longitude,  the  apparent  time 
must  be  subtracted  from  12  hours  and  the  remainder  turned 
into  degrees. 

Remarks.— The  time  may  also  be  converted  into  degrees  by  the 
use  of  the  rule  given  under  the  head  of  Arithmetic  of  Naviga- 
tion. 

Observe  the  first  altitude  about  half  an  hour  before  noon. 

If,  after  measuring  the  first  altitude,  the  ship  sails  toward  the 
sun,  then  the  original  altitude  must  be  increased  one  minute  of 
arc  for  every  mile  sailed  between  the  two  sights.  To  make  this 
clear,  let  it  be  supposed  that  the  first  altitude  read  20°  30'  and  that 
in  the  interval  between  the  sights  the  ship  sailed  ten  miles  toward 
the  sun — the  instrument  must  be  set  to  read  20*40'  and  the  sec- 
ond altitude  measured  by  that.  If,  on  the  other  hand,  the  ship 
sails  away  from  the  sun  after  measuring  the  first  altitude,  then 
the  reading  must  be  decreased  one  minute  of  arc  for  every  mile 
sailed  in  the  interval,  and  the  second  altitude  measured  accord- 
ingly. 

Longitude  by  One  Altitude  of  the  Sun. — Observe  an  altitude 
(see  Altitude)  and  note  the  hour,  minute,  and  second  shown  by 
chronometer  at  the  instant  of  contact,  and  correct  the  latter  for 
its  rate  ;  also  correct  the  altitude  and  the  sun's  declination  (see 
Rate  ;  Corrected  Altitude  ;  Declination).  Next  obtain  the  sun's 
polar  distance  (see  Polar  Distance)  and  add  to  it  the  true  central 
altitude  and  the  latitude  by  dead-reckoning,  then  divide  the  sum 
of  these  three  quantities  by  2,  and  from  the  half  sum  so  obtained 
subtract  the  true  central  altitude,  calling  the  answer  the  remain- 
der. Now  select  (Table  44)  the  logarithms,  secant  of  the  latitude, 
cosecant  of  the  polar  distance,  cosine  of  the  half  sum,  and  sine 


THE  NAVIGATOR'S  POCKET-BOOK  93 

of  the  remainder — rejecting  the  index  of  each  log.  when  it  is 
more  than  9  (see  Logarithm).  Add  these  four  logs,  together, 
divide  by  2,  and  the  answer  will  be  the  sine  of  the  apparent 
time  at  ship  when  the  sight  was  taken.  With  this  sine,  select 
(Table  44)  the  time  standing  against  it,  taking  same  from  the  A.M. 
column  if  the  observation  is  made  in  the  morning,  but  from  the 
P.M.  column  if  made  in  the  afternoon.  If  the  log.  sine  cannot  be 
perfectly  matched,  then  select  the  time  for  the  nearest  corre- 
sponding log.  and  correct  the  time  as  explained  under  the  head  of 
Logarithms.  Apply  the  corrected  equation  of  time  (see  Equa- 
tion of  Time)  to  the  apparent  time  at  ship  according  to  the  head- 
ing of  the  almanac  column,  so  as  to  convert  it  into  mean  time  at 
ship.  The  difference  between  the  mean  time  at  ship  and  the 
mean  time  at  Greenwich  will  be  the  longitude  in  time,  which 
will  be  turned  into  degrees  either  by  the  use  of  Table  7  or  by  the 
rule  given  under  the  head  of  Arithmetic  of  Navigation. 

Remarks. — If  one  time  is  A.M.,  and  the  other  time  P.M.,  it  will 
be  necessary  to  add  twelve  hours  to  the  P.M.  time  before  subtract- 
ing—for instance,  if  the  time  at  ship  is  10  A.M.  and  the  time  at 
Greenwich  2  P.M.,  the  times  are  four  hours  apart,  and  this  is 
found  by  calling  the  Greenwich  time  fourteen  hours  and  sub- 
tracting the  ten  hours  from  it. 

The  best  time  to  take  sights  for  longitude  is  when  the  sun  is 
either  rising  or  falling  rapidly,  so  that  a  considerable  change  of 
altitude  will  only  affect  the  time  to  a  small  extent ;  but  do  not 
use  an  altitude  of  less  than  10°,  owing  to  the  uncertainty  of  the 
refraction. 

When  the  sun  can  be  observed  exactly  in  the  prime  vertical 
(when  it  bears  true  east  or  west)  an  error  of  a  considerable  num- 
ber of  miles  in  the  latitude  by  dead-reckoning  will  not  produce 
a  wrong  result  in  the  longitude.  (See  Prime  Vertical.) 


94  THE  NAVIGATOR'S  POCKET-BOOK 

If  it  is  desired,  several  altitudes  may  be  observed  in  quick  suc- 
cession, noting  the  corresponding  times  by  chronometer,  and  the 
sum  of  these  altitudes  and  times  divided  by  the  whole  number  of 
altitudes  taken  so  as  to  obtain  the  mean  of  the  altitudes  corre- 
sponding to  the  mean  of  the  times.  This  process  will  eliminate 
any  small  error  that  might  creep  into  a  single  altitude  and 
time. 

In  order  to  understand  the  manner  in  which  longitude  is  car- 
ried forward  or  back  to  noon  from  an  A.M.  or  a  P.M.  sight,  see 
explanation  given  under  heading  of  Log-Book. 

Longitude  at  Sunrise  or  Sunset. — Observe  the  sun's  upper 
or  lower  limb  to  touch  the  horizon  at  rising  or  setting  and  note 
the  hour,  minute,  and  second  shown  by  chronometer  at  the  in- 
stant of  contact,  and  correct  the  latter  for  its  rate  ;  also  correct 
the  sun's  declination  and  obtain  the  polar  distance  (see  Rate  ; 
Declination  ;  Polar  Distance).  Now  add  together  the  latitude 
by  dead-reckoning  and  the  polar  distance  and  from  their  sum 
subtract  21'  if  the  contact  of  the  lower  limb  was  observed,  but 
subtract  53'  if  the  contact  of  the  upper  limb  was  noted.  Now  di- 
vide the  balance  by  2,  and  to  this  half-sum  add  21'  for  a  lower- 
limb  calculation,  but  add  53'  for  an  upper-limb  calculation. 
From  this  point  select  the  various  logarithms  and  proceed  to 
find  the  longitude  in  precisely  the  same  manner  as  directed  in 
the  preceding  rule  under  the  head  of  Longitude  by  One  Al- 
titude of  the  Sun. 

Remarks.— -The  particular  value  of  this  working  is  in  the 
fact  that  the  sextant  is  dispensed  with  ;  consequently,  if  that 
instrument  meets  with  an  accident  and  is  rendered  useless,  the 
navigator  is  not  left  dependent  upon  his  dead-reckoning  for 
longitude. 

By  employing  a  marine  glass,  the  contact  of  the  sun's  limb 


THE  NAVIGATOR'S  POCKET-BOOK 


95 


with  the  horizon  may  be  more  accurately  determined  than  by 
the  unaided  eye. 

Longitude  by  an  Altitude  near  Sunrise  or  Sunset, — At  the 
time  that  the  centre  of  the  sun  is  in  the  true  horizon  (90°  from 
the  zenith)  the  lower  limb  has  an  apparent  altitude  of  about  19' 
and  the  upper  limb  about  46'. 

A  little  time  before  sunrise  or  sunset,  consult  the  following 
table  and  select  under  the  figures  most  nearly  corresponding  to 
the  height  of  eye,  the  altitude  for  the  sun's  lower  or  upper  limb 
as  desired,  and  place  same  on  the  arc  of  the  sextant : 


Sun's  Semi- 
diameter. 

Height  of  Eye,  13  feet. 

Sun's  Semi- 
diameter. 

Height  of  Eye,  21  feet. 

Altitude  of 
Sun's  Upper 
Limb. 

Altitude  of 
Sun's  Lower 
Limb. 

Altitude  of 
Sun's  Upper 

Limb. 

Altitude  of 
Sun's  Lower 
Limb. 

/     // 
15  45 
16  00 
16  15 

/     // 
46  00 
46  10 
46  20 

/     // 
18  20 
18  10 
18  00 

/     // 
15  45 
16  00 
16  15 

/      // 

47  00 
47  10 
47  20 

/     // 
19  20 
19  10 
19  00 

With  the  sextant  set  to  the  required  altitude,  note  when  the 
image  of  the  sun's  proper  limb  is  in  perfect  contact  with  the 
horizon  line,  and  observe  the  hour,  minute,  and  second  shown 
by  chronometer  at  the  instant  of  kissing.  Correct  the  chronom- 
eter for  its  rate  (see  Rate)  and  add  together  the  logarithms  tan- 
gent of  the  ship's  latitude  (by  dead-reckoning)  and  tangent  of 
the  sun's  corrected  declination  (see  Declination)  ;  their  sum,  re- 
jecting ten  from  the  index,  will  be  the  logarithm  sine  of  an 
angle,  which  select  from  Table  44  and  turn  into  time  by  Table  7, 
or  by  the  rule  under  Arithmetic  of  Navigation.  If  the  latitude 
and  the  sun's  declination  are  of  the  same  name  (north  or  south) 
add  the  time  so  found  to  six  hours  at  sunset,  but  subtract  it  from 
six  hours  at  sunrise.  If  the  latitude  and  declination  are  of  con- 


96  THE  NAVIGATOR'S.  POCKET-BOOK 

trary  names,  add  the  given  time  to  six  hours  at  sunrise,  but  sub- 
tract it  from  six  hours  at  sunset.  To  this  apparent  time  at  ship 
apply  the  equation  of  time  (see  Equation  of  Time)  so  as  to  con- 
vert it  into  mean  time  at  ship,  after  which  take  the  difference  be- 
tween it  and  the  Greenwich  mean  time  and  turn  the  result  into 
degrees,  which  will  be  the  longitude  of  the  ship. 

Remark. — This  method  should  not  be  used  beyond  the  par- 
allels of  40°  north  and  south. 

Longitude  by  One  Altitude  of  the  Moon. — Observe  an  alti- 
tude (see  Altitude)  and  note  the  chronometer  at  the  instant  of 
contact,  to  which  time  apply  the  rate  correction,  then  turn  this 
Greenwich  mean  time  into  astronomical  mean  time  (see  Astro- 
nomical Time)  and  next  correct  the  moon's  altitude  and  declina- 
tion (see  Corrected  Altitude  ;  Declination).  Now  obtain  the 
moon's  polar  distance  (see  Polar  Distance)  and  add  to  it  the 
moon's  corrected  altitude  and  the  latitude  by  dead-reckoning ; 
divide  the  sum  of  these  three  quantities  by  2  and  from  this 
half-sum  subtract  the  moon's  corrected  altitude.  Select  (Table 
44)  the  logarithms  secant  of  latitude,  cosecant  of  polar  distance, 
cosine  of  the  half-sum  and  sine  of  the  remainder,  rejecting  the 
index  of  each  log.  when  it  exceeds  nine.  Add  these  four  logs, 
together,  divide  by  2,  and  the  answer  will  be  the  sine  of  a  time 
which  will  be  selected  from  the  P.  M.  column  (Table  44).  Apply 
this  time  to  the  moon's  corrected  right  ascension  (see  Right  As- 
cension), subtracting  it  if  the  moon  is  east  of  the  meridian,  but 
adding  it  if  the  moon  is  west  of  the  meridian — the  difference  or 
sum  will  be  the  right  ascension  of  the  meridian,  from  which  (in- 
creased by  twenty-four  hours  if  necessary  for  the  purposes  of 
subtraction)  subtract  the  sun's  corrected  right  ascension,  and 
the  remainder  will  be  the  astronomical  apparent  time  at  ship. 
To  this  apply  the  corrected  equation  of  time  (see  Equation  of 


THE  NAVIGATOR'S  POCKET-BOOK  97 

Time)  according  to  heading  of  the  almanac  column  and  the 
answer  will  be  the  astronomical  mean  time  at  ship  ;  then 
the  difference  between  this  and  the  astronomical  mean  time 
at  Greenwich  will  be  the  longitude  in  time,  which  turned 
into  degrees  (either  by  the  use  of  Table  7  or  by  the  rule  given 
under  the  head  of  Arithmetic  of  Navigation)  will  be  the  lon- 
gitude. 

Remarks.-—  When  the  astronomical  mean  time  at  the  ship  and 
the  astronomical  mean  time  at  Greenwich  are  of  different  dates, 
it  will  be  necessary  to  add  twenty-four  hours  to  the  time  of  the 
latest  date  for  the  purposes  of  subtraction  between  them,  then 
the  answer  will  be  the  longitude  in  time. 

As  explained  for  the  sun,  the  best  hour  to  observe  a  time 
altitude  of  a  heavenly  body  is  when  it  is  the  nearest  to  the  prime 
vertical.  (See  Prime  Vertical.) 

If  desired,  several  altitudes  of  the  moon  may  be  observed  in 
quick  succession  and  the  corresponding  times  by  the  chronom- 
eter noted,  then  the  mean  of  these  altitudes  and  times  accepted 
as  a  base  from  which  to  calculate  the  longitude.  As  explained 
for  the  sun,  this  will  eliminate  any  small  error  as  regards  the 
altitude  and  noting  of  the  time. 

If  the  log.  sine  of  the  time  cannot  be  matched,  correct  the  time 
given  in  the  P.M.  column  according  to  the  rule  given  under  the 
head  of  Logarithms. 

Longitude  by  One  Altitude  of  a  Planet. — This  problem  is  to 
be  worked  in  the  same  way  as  the  one  described  immediately 
preceding  for  the  moon,  simply  substituting  the  planet's  polar 
distance  and  right  ascension,  as  may  be  seen  by  the  following 
rule  : 

Add  together  the  planet's  corrected  altitude,  the  latitude  by 
dead-reckoning,  and  the  planet's  polar  distance ;  divide  by  2 
7 


98  THE  NAVIGATOR'S  POCKET-BOOK 

and  from  the  half-sum  subtract  the  corrected  altitude  ;  select 
from  Table  44  the  logs,  secant  of  latitude,  cosecant  of  polar  dis- 
tance, cosine  of  half-sum,  and  sine  of  remainder  ;  add  these  four 
logs,  and  divide  by  2,  calling  the  answer  the  sine  of  a  time, 
which  take  out  in  the  P.M.  column,  Table  44,  and  apply  said 
time  to  the  planet's  corrected  right  ascension,  subtracting  it  if 
the  planet  is  east  of  the  meridian,  but  adding  it  if  the  planet  is 
west  of  the  meridian — the  difference,  or  sum,  will  be  the  right 
ascension  of  the  meridian,  from  which  (increased  by  twenty- 
four  hours  if  necessary  for  the  purposes  of  subtraction)  subtract 
the  sun's  corrected  right  ascension  and  the  answer  will  be  the 
astronomical  apparent  time  at  the  ship,  to  which  apply  the  cor- 
rected equation  of  time,  then  find  the  difference  between  this 
astronomical  mean  time  at  ship  and  the  astronomical  mean  time 
at  Greenwich  ;  the  answer  will  be  the  longitude  in  time,  which 
convert  into  degrees. 

Longitude  by  One  Altitude  of  a  Star. — As  explained  for  a 
planet,  this  problem  is  worked  in  the  same  manner  as  the  moon, 
it  simply  being  necessary  to  substitute  the  star's  polar  distance 
and  right  ascension  ;  but  it  is  to  be  explained  that  corrections 
for  the  declination  and  right  ascension  of  stars  are  too  small  to 
be  considered,  simply  accepting  the  same  for  the  given  year 
being  all  that  is  necessary.    (See  Fixed  Stars.) 
Longitude  by  Dead-Reckoning.— (See  Dead-Reckoning.) 
Longitude  by  the  Artificial  Horizon.— (See  Artificial  Hori- 
zon.) 

LONGITUDE  IN  ARC.— The  position  or  distance  of  a 
vessel  east  or  west  of  a  given  prime  meridian,  expressed  in 
degrees,  minutes,  and  seconds  of  angular  measure. 

LONGITUDE  IN  TIME — The  position  or  distance  of  a 


THE  NAVIGATOR'S  POCKET-BOOK  99 

vessel  east  or  west  of  a  given  prime  meridian,  expressed  in  hours, 
minutes,  and  seconds  of  time  measure. 

LOST  DAY — (See  Circumnavigator's  Day.) 
LOWER  LIMB.— (See  Upper  Limb.) 

LOWER  TRANSIT.— The  passage  of  a  heavenly  body  over 
the  meridian  180°  distant  from  the  meridian  of  the  upper  transit. 
In  high  northern  and  southern  latitudes  at  certain  times  of  the 
year  the  sun  and  moon  do  not  set  during  the  twenty-four  hours, 
but  circle  around  the  heavens,  at  all  times  in  view  of  the  ob- 
server ;  consequently  they  are  then  seen  at  the  period  of  their 
lower  as  well  as  upper  transit.  The  Nautical  Almanac  gives  the 
astronomical  times  of  the  upper  transit  of  heavenly  bodies,  which 
takes  place  when  the  bodies  are  moving  (apparently)  from  east  to 
west.  (See  Upper  Transit ;  Midnight  Sun.) 

LOW  LATITUDES.— Parallels  in  the  vicinity  of  the  equa- 
tor. (See  High  Latitudes.) 

L'S  OF  NAVIGATION.— Lead,  Lights,  Lookout,  Latitude, 
Longitude. 

LUBBER'S  POINT.— The  vertical  black  line  painted  on 
the  inside  surface  of  the  compass  bowl,  and  which  represents 
the  ship's  head  and  the  line  of  the  keel. 

LUNAR. — Relating  to  the  moon. 

LUNAR  DAY — The  interval  of  time  between  two  successive 
transits  of  the  moon  over  the  same  meridian. 

LUNAR  DISTANCE.— The  angular  measurement  of  the 
moon  from  another  heavenly  body. 

LUNAR  INEQUALITY.— A  variation  in  the  moon's  mo- 
tion which  depends  upon  its  distance  from  the  sun. 


100  THE  NAVIGATOK'S  POCKET-BOOK 

MAGNET. — An  ore  that  attracts  iron.  The  properties  of  a 
magnet  are  that,  with  the  exception  of  the  oxides,  it  attracts 
iron  in  all  of  its  various  states.  If  a  bar  of  steel  is  charged  with 
magnetism,  either  by  a  magnet  or  by  a  dynamo,  then  suspended, 
horizontally  balanced  by  a  slender  thread,  the  bar  will  indicate 
the  magnetic  meridian.  What  is  known  as  an  artificial  magnet 
is  a  bar  or  mass  of  iron  or  steel  into  which  the  magnetic  prop- 
erty has  been  introduced  by  the  presence  of,  or  contact  with,  a 
body  possessing  the  same. 

MAGNETIC. — Having  power  to  attract  iron. 

MAGNETIC  AMPLITUDE.— The  bearing  by  compass  of 
a  heavenly  body  at  rising  and  setting,  or  an  arc  of  the  horizon 
intercepted  between  the  body  in  its  rising  and  setting  and  the 
east  and  west  compass  points. 

MAGNETIC  AZIMUTH — The  arc  of  the  horizon  inter- 
cepted between  the  vertical  circle  and  the  magnetic  meridian, 
or  the  bearing  by  compass  of  a  heavenly  body,  calculated  from 
the  north  point  in  north  latitudes  and  the  south  point  in  the 
southern  hemisphere. 

MAGNETIC  BEARING. —  A  bearing  according  to  the 
compass,  or  the  direction  pointed  out  by  the  magnetic  needle. 

MAGNETIC  DIP.— A  property  belonging  to  the  magnetic 
needle,  whereby  one  of  its  poles  (ends)  inclines  toward  the 
earth,  while  the  other  pole  is  repelled  or  elevated. 

MAGNETIC  EQUATOR.— A  line  passing  through  those 
points  on  the  surface  of  the  earth  where  the  dipping  needle  rests 
in  a  horizontal  position.  (See  Compass.) 

MAGNETIC  INDUCTION.— Communication  of  magnetism 
from  a  magnet  to  a  body  of  iron  in  its  vicinity,  although  per- 


THE  NAVIGATOR'S,  POCKET-BOOK  101 

haps  not  touching  it.  The  communication  of  magnetism  from 
the  earth  (which  is  a  huge  magnet  in  itself)  to  the  hulls  of  iron 
and  steel  vessels  is  known  as  the  earth's  induction. 

MAGNETIC  MERIDIAN.— A  vertical  circle  in  the  heav- 
ens which  intersects  the  horizon  in  the  magnetic  poles  ;  or  it  may 
be  defined  as  the  natural  direction  pointed  out  by  the  compass 
needle  when  allowed  to  turn  freely  and  removed  from  the  effects 
of  deviation  and  local  attraction. 

MAGNETIC  NEEDLE.— The  slender  piece  of  magnetized 
steel  to  which  the  compass  card  is  fastened. 

MAGNETIC  POLES.— Two  places  on  the  earth's  surface 
where  the  dipping  needle  assumes  a  position  perpendicular  to 
the  horizon  and  shows  a  dip  of  90°.  The  north  magnetic  pole  is 
situated  on  the  parallel  of  70°  north  and  on  the  meridian  of  97° 
west ;  the  south  magnetic  pole  on  the  parallel  of  73°  south  and 
on  the  meridian  of  146°  east. 

MAGNITUDE. — According  to  their  brilliancy  the  stars  are 
classed  as  of  the  first,  second,  third,  fourth,  fifth,  sixth,  and 
seventh  magnitudes.  Stars  beyond  the  seventh  magnitude  can- 
not be  seen  with  the  unaided  eye,  and  are  known  as  telescopic 
stars. 

MAKING  THE  LAND.— A  landfall  ;  to  obtain  the  first 
view  of  land. 

MAST-HEAD  ANGLES.— To  measure  the  distance  between 
the  observer's  ship  and  another  vessel,  it  is  only  necessary  to 
know  the  height  of  her  mast  or  smoke-stack,  and  the  vertical 
angle  of  the  same  measured  to  the  surface  of  the  water — to  her 
water-line.  If  the  image  of  the  truck,  or  the  rim  of  the  smoke 
funnel  is  thrown  to  the  water-line  by  the  sextant,  and  this  angle 


102  TIJI;  ^AYIGATOR'S  PQCKET-BOOK 

referred  to  the  danger-angle  tables  in  the  back  of  this  book,  the 
distance  of  the  vessel  will  at  once  be  obtained  by  simple  inspec- 
tion. 

To  tell,  when  in  a  race,  if  the  distance  between  two  vessels  is 
increasing  or  decreasing,  note  several  mast-head  angles.  If  the 
angles  increase  it  proves  that  the  two  vessels  are  drawing  nearer, 
but  if  the  angles  decrease  the  vessels  are  separating  more  and 
more.  (See  Danger- Angle  Tables.) 

MAST-HEAD  COMPASS.— A  compass  hung  at  the  lower- 
mast-head  so  as  to  remove  it  out  of  the  influence  of  the  magnet- 
ism in  the  ship's  iron.  (See  Elevator  Compass.) 

MEAN  NOON. — The  time  that  the  mean  sun  is  supposed  to 
cross  the  observer's  meridian. 

MEAN  SOLAR  TIME — Time  calculated  by  the  motion  of 
the  mean  sun.  All  watches  and  clocks  represent  mean  solar 
time. 

MEAN  SUN. — An  imaginary  sun  which  is  supposed  to 
move  uniformly  and  to  cross  the  same  meridian  the  same  time 
every  day,  thus  giving  a  value  of  exactly  twenty-four  hours  to 
the  day.  This  mean  or  fictitious  sun  sometimes  crosses  the 
observer's  meridian  a  little  in  advance  of  the  true  sun,  and  at 
other  times  a  little  after  it,  and  this  difference  or  interval  between 
the  real  and  imaginary  suns  is  known  as  the  equation  of  time. 

By  referring  to  the  almanac  it  will  be  seen  that  four  times  in 
each  year  the  real  and  imaginary  suns  pass  the  same  meridian  at 
the  same  time ;  namely,  about  April  14th,  June  13th,  August 
31st,  and  December  23d  ;  consequently  on  these  days  the  equa- 
tion of  time  may  be  considered  as  zero.  The  maximum  equa- 
tion of  time  is  about  16  m.  20  sec. 


THE  NAVIGATOR'S  POCKET-BOOK:  103 

MEAN  TIME — Same  as  mean  solar  time. 
MERCATOR'S  CHART.— (See  Chart.) 

MERCATOR'S  SAILING — A  method  of  finding  (indepen 
dent  of  the  parallel  rules  and  dividers)  the  true  course  and  dis- 
tance between  two  places  by  employing  meridional  parts  instead 
of  the  middle  latitude. 

Rule. — Find  the  difference  of  latitude  and  the  difference  of 
longitude  between  the  two  places.  If  the  two  latitudes  have 
the  same  name  (both  north  or  both  south)  subtract  one  from 
the  other,  but  if  they  have  different  names  add  them  together. 
Now  multiply  the  degrees  of  the  answer  by  60  to  convert  them 
into  miles  and  add  in  the  minutes  as  they  represent  miles  ;  the 
answer  will  be  the  difference  of  latitude.  Proceed  to  find  the 
difference  of  longitude  in  the  same  way — add  the  longitudes  to- 
gether if  of  different  names,  but  subtract  between  them  if  of  the 
same  name. 

Turn  to  Table  3  and  select  the  meridional  parts  for  the  degrees 
and  minutes  of  each  latitude,  and  if  the  latitudes  are  of  differ- 
ent names,  add  the  meridional  parts,  but  if  the  latitudes  are  of 
the  same  name,  subtract  one  of  the  meridional  parts  from  the 
other.  In  other  words,  if  the  latitudes  were  added  the  me- 
ridional parts  must  be  added,  and  if  the  latitudes  were  subtract- 
ed the  meridional  parts  must  be  subtracted.  4 

With  the  meridional  difference  of  latitude  and  the  difference 
of  longitude  turn  to  Table  2  and  make  them  compare  by  seeking 
in  the  latitude  column  for  the  meridional  difference  of  latitude 
and  in  the  departure  column  opposite  for  the  difference  of  longi- 
tude. On  the  page  of  their  comparison  the  true  or  geographical 
course  between  the  two  places  will  be  read  in  degrees  from  the 
top  of  the  page  if  the  meridional  difference  of  latitude  is  greater 


104  THE  NAVIGATOR'S  POCKET-BOOK 

than  the  difference  of  longitude,  but  it  will  be  read  from  the 
bottom  of  the  page  if  the  difference  of  longitude  exceeds  the 
meridional  difference  of  latitude. 

On  the  same  page  apply  the  proper  difference  of  latitude  in 
the  latitude  column  from  that  part  of  the  page  (top  or  bottom) 
where  the  course  was  read,  and  opposite  to  the  left  in  the  dis- 
tance column  will  be  found  the  distance  in  nautical  miles  for 
the  course  found,  which,  in  other  words,  will  be  the  number  of 
miles  required  to  be  sailed  on  a  direct  line  between  the  ship's 
place  and  the  point  sought. 

The  variation  (also  the  deviation,  if  any  exists)  of  the  compass 
must  be  applied  to  the  true  course  in  order  to  convert  the  same 
into  a  magnetic  course,  or  the  course  necessary  to  be  steered  by 
the  ship's  compass  in  order  to  make  the  true  track. 

To  Apply  Variation. — Suppose  the  true  course  found  is 
southeast,  and  the  chart  informs  us  that  in  the  ship's  locality 
there  is  one  point  of  westerly  variation.  The  effect  of  this  is 
that  the  southeast  point  of  the  compass  is  swung  so  that  it  really 
points  southeast -by-east,  and  in  order  to  make  a  true  southeast 
course  the  ship  must  be  steered  southeast-by- south  according 
to  the  compass. 

Rule.—K  simple  rule  to  remember  for  converting  a  true 
course  into  a  magnetic  course  is  to  allow  westerly  variation 
away  from  the  true  course  in  the  direction  that  the  hands  of  a 
watch  revolve,  and  easterly  variation  contrary,  or  against  the 
hands  of  a  watch. 

To  Apply  Deviation.— If  deviation  exists  for  the  magnetic 
course  found,  the  latter  must  have  the  deviation  applied  to  it  on 
exactly  the  same  principle  as  explained  for  variation.  For  ex- 
ample, we  will  say  that  the  magnetic  course  found  is  southeast- 
by-south,  and  that  there  is  one  point  of  westerly  deviation  to  be 


THE  NAVIGATOR'S  POCKET-BOOK  105 

allowed  for  when  the  ship's  head  is  on  that  course.  The  com- 
pass course  to  be  steered  in  this  case  is  south-southeast,  in  order 
to  make  a  correct  magnetic  course  of  southeast-by-south. 

Remarks.  —  The  variation  must  always  be  applied  before 
applying  the  deviation. 

It  is  to  be  remembered  that  the  compass  course  must  be  re- 
shaped as  often  as  the  variation  changes.  For  example,  we  will 
say  that  the  true  course  from  Sandy  Hook  to  Bermuda  Island  is 
S.  42°  E.,  and  that  in  the  vicinity  of  Sandy  Hook  the  variation 
of  the  compass  is  8°  westerly.  The  magnetic  course  in  this  case 
is  S.  34°  E.,  which  equals  southeast-by-south.  To  this  course 
we  apply  the  deviation  correction  (if  any  exists)  given  by  our 
deviation  card  or  found  by  observation,  and  then  we  hold  the 
indicated  compass  course  until  we  reach  a  latitude  and  longitude 
where  the  variation  of  the  compass  is  shown  to  change,  when  it 
becomes  necessary  for  us  to  apply  the  new  variation  given  by 
the  chart  and  change  the  course  accordingly. 

When,  by  reason  of  opposing  winds  or  other  causes,  the  vessel 
does  not  keep  on  the  direct  course  for  the  port  bound  to,  then 
the  whole  process  of  laying  out  the  course  must  be  gone  through 
with  again.  This  may  happen  many  times  before  the  port  is 
reached. 

Mercator's  Sailing  is  to  be  preferred  to  Middle  Latitude  Sail- 
ing, unless  the  course  is  nearly  east  or  west. 

MERCURIAL  BAROMETER.  —  An  instrument  which 
shows  the  pressure  of  the  air  or  weight  of  the  atmosphere.  It 
is  a  tube  thirty-four  inches  long,  closed  at  the  top  and  exhausted 
of  air.  The  lower  end  of  this  tube  is  immersed  in  a  cup  or 
cistern  of  mercury,  and  the  pressure  of  the  atmosphere  causes 
the  fluid  to  ascend  in  the  slender,  hollow  column.  The  varia- 
tion in  height  of  the  mercury  is  dependent  upon  the  weight  or 


106  THE   NAVIGATOR^  POCKET-BOOK 

pressure  of  the  atmosphere.  These  variations  are  measured  by 
aid  of  a  scale  graduated  in  inches  and  parts  and  fixed  against 
the  tube.  When  the  mercury  in  the  cistern  is  pressed  down 
by  the  air  the  mercury  rises  in  the  exhausted  tube,  but  when 
the  mercury  in  the  cistern  rises  on  account  of  diminished  press- 
ure of  air  the  mercury  in  the  tube  falls.  (See  Barometer.) 

MERIDIAN. — The  highest  point  of  the  great  arc  described 
by  a  heavenly  body  from  its  rising  to  its  setting.  When  the 
sun  crosses  the  observer's  meridian  it  is  12  o'clock,  apparent 
noon,  at  his  place.  A  meridian  is  an  imaginary  great  circle  of 
the  sphere  extending  from  pole  to  pole.  (See  Circumnavi- 
gator's Day  ;  Prime  Meridian  ;  Secondary  Meridians  ;  Tertiary 
Meridians. ) 

MERIDIAN  ALTITUDE. — The  angular  height  of  a  heav- 
enly body  from  the  horizon  line  at  the  time  the  body  is  crossing 
the  meridian.  (See  Altitude  ;  Latitude.) 

MERIDIAN  PASSAGE. — The  crossing  of  a  heavenly  body 
over  the  meridian  of  the  observer.  (See  Lower  Transit ;  Upper 
Transit.) 

MERIDIAN  SAILING. — Sailing  on  a  meridian  ;  sailing 
true  north  or  south.  (See  Parallel  Sailing.) 

MERIDIONAL  DIFFERENCE.— The  quantity  given  in 
Table  3,  which  bears  the  same  proportion  to  the  difference  of 
latitude  that  the  difference  of  longitude  bears  to  the  departure. 

MERIDIONAL  PARTS. — Degrees  of  latitude  increased 
from  their  natural  lengths  more  and  more  as  the  equator  is 
receded  from,  and  the  lengths  of  the  small  portions  of  the 
meridian  thus  increased,  expressed  in  minutes  of  the 
are  called  meridional  parts.  (Table  3.) 


THE  NAVIGATOR'S  POCKET-BOOK  107 

METEOROLOGY.— The  science  of  the  atmosphere  and  its 
phenomena.  (See  Log-Book  ;  Weather.) 

MIDDLE  LATITUDE. — Half  of  the  sum  of  two  latitudes 
of  the  same  name,  but  half  of  the  figures  left  after  subtracting 
between  two  latitudes  of  different  names.  The  middle  latitude 
between  20°  north  and  30°  north  is  25°  north.  The  middle  lati- 
tude between  20°  north  and  30°  south  is  5°  south. 

MIDDLE-LATITUDE  SAILING.— The  method  of  finding 
(independent  of  the  parallel  rules  and  dividers)  the  true  course 
and  the  distance  between  two  places  by  employing  the  middle 
parallel  between  them. 

Rule.— Find  the  difference  of  latitude  and  the  difference  of 
longitude  between  the  two  places.  If  the  two  latitudes  have 
the  same  name  (both  north  or  both  south)  subtract  one  from  the 
other ;  but  if  they  have  different  names  add  them  together. 
Now  multiply  the  degrees  of  the  answer  by  60  to  convert  them 
into  miles,  and  add  in  the  minutes  as  they  represent  miles  ;  the 
answer  will  be  the  difference  of  latitude.  Proceed  to  find  the 
difference  of  longitude  in  the  same  way  :  add  the  longitudes  to- 
gether if  of  different  names,  but  subtract  between  them  if  of  the 
same  name. 

Next,  to  find  the  middle  latitude  :  if  the  two  latitudes  are  of 
the  same  name  add  them  together  and  divide  by  2  ;  but  if  they  are 
of  different  names  subtract  one  from  the  other  and  divide  by  2. 
The  answer  will  be  the  parallel  equidistant  between  the  place 
of  the  ship  and  the  port  sought. 

With  this  middle  latitude  turn  to  Table  2,  and  on  the  page 
marked  with  the  degrees  of  the  middle  latitude  apply  the  dif- 
ference of  longitude  in  the  distance  column,  and  opposite  to  the 
right  in  the  latitude  column  (reading  from  the  top  of  the  page  if 


108  THE  NAVIGATOR'S  POCKET-BOOK 

the  degrees  were  found  there,  but  from  the  bottom  of  the  page 
if  the  degrees  were  found  there)  will  stand  the  departure,  or  the 
number  of  nautical  miles  in  an  east  and  west  line  between  the 
ship  and  the  sought-for  port. 

Now,  with  the  difference  of  latitude  and  the  departure  make 
them  compare  in  Table  2  in  their  respective  columns  opposite 
one  another,  and  in  the  distance  column  to  the  left  will  be  seen 
the  direct  distance  to  be  sailed  in  nautical  miles,  and  the  true  or 
geographical  course  between  the  two  places  will  be  read  in  de- 
grees from  the  top  of  the  same  page  if  the  difference  of  lati- 
tude is  greater  than  the  departure,  but  the  course  will  be  read 
from  the  bottom  of  the  same  page  if  the  departure  exceeds  the 
difference  of  latitude. 

The  variation  (also  the  deviation,  if  any  exists)  of  the  compass 
must  be  applied  to  the  true  course  in  order  to  convert  the  same 
into  a  magnetic  course,  or  the  course  necessary  to  be  steered  by 
the  ship's  compass,  in  order  to  make  the  true  track. 

To  Apply  Variation.-— Suppose  the  true  course  found  is 
south  and  the  chart  informs  us  that  in  the  ship's  locality  there 
is  one  point  of  easterly  variation.  The  effect  of  this  is  that  the 
compass  south  point  is  swung  so  that  it  really  points  south-by 
west,  and  in  order  to  make  a  true  south  course  we  must  steer 
south-by-east  by  the  compass. 

Rule. — A  simple  rule  to  remember  for  converting  a  true  course 
into  a  magnetic  course  is  to  allow  the  amount  of  westerly  varia- 
tion away  from  the  true  course  in  the  direction  that  the  hands 
of  a  watch  revolve,  and  easterly  variation  contrary  or  against 
the  hands  of  a  watch. 

To  Apply  Deviation. — If  deviation  exists  for  the  magnetic 
course  found,  the  latter  must  have  the  deviation  applied  to  it  on 
exactly  the  same  principle  as  explained  for  variation.  For  ex- 


THE  NAVIGATOR'S  POCKET-BOOK  109 

ample,  we  will  say  that  the  magnetic  course  found  is  northeast, 
and  that  there  is  half  a  point  of  westerly  deviation  to  be  allowed 
for  when  the  ship's  head  is  on  that  course.  The  compass  course 
to  be  steered  in  this  case  is  northeast-half-east,  in  order  to  make 
a  correct  magnetic  course  of  northeast. 

Remarks. — The  variation  must  always  be  applied  before  ap- 
plying the  deviation. 

It  must  be  borne  in  mind  that  the  compass  course  is  to  be  re- 
shaped as  often  as  the  variation  changes.  For  example,  we 
will  say  that  the  true  course  found  is  N.  45°  E.,  and  that  in  the 
locality  of  the  ship  the  variation  of  the  compass  is  6°  easterly. 
The  magnetic  course  in  this  case  is  N.  39°  E.,  which  equals 
northeast  half-north.  To  this  course  we  apply  the  deviation 
correction  (if  any  exists)  given  by  our  deviation  card  or  found 
by  observation,  and  then  we  hold  the  indicated  compass  course 
until  we  reach  a  latitude  and  'longitude  where  the  variation  of 
the  compass  is  shown  to  change,  when  it  becomes  necessary 
to  apply  the  new  variation  given  by  the  chart,  and  change  the 
course  accordingly. 

When  by  reason  of  head  winds  or  other  causes  the  vessel 
does  not  keep  on  the  direct  course  for  the  port  to  which  she  is 
bound,  then  the  whole  process  of  laying  out  the  course  must  be 
gone  through  with  again.  This  may  occur  many  times  before 
the  port  is  reached. 

Middle-Latitude  Sailing  is  to  be  preferred  to  Mercator's  Sail- 
ing when  the  course  is  nearly  east  or  west. 

MIDDLE  POINT.— (See  Drift.) 

MIDNIGHT  SUN.— As  explained  under  the  head  of  Lower 
Transit,  in  high  latitudes  during  the  summer  season  there  are 
times  when  the  sun  does  not  set  for  the  observer  during  the 


110  THE  NAVIGATOR'S  POCKET-BOOK 

twenty-four  hours,  and  on  account  of  crossing  at  12  o'clock  at 
night  the  meridian  180°  distant  from  the  meridian  which  it 
crossed  when  it  made  its  upper  transit,  it  derives  its  name  of 
the  midnight  sun. 

MILE. — A  statute  mile  is  5,280  feet ;  a  nautical  or  geograph- 
ical mile  6,082.66  feet ;  the  latter  is  also  called  a  knot. 

MINUTE. — A  mile  of  latitude  and  a  minute  of  latitude  are 
of  equal  value— 6,082.66  feet.  A  minute  of  longitude  varies 
in  value  according  to  the  distance  from  the  equator.  At  the 
equator  a  minute  of  longitude  is  equal  to  a  minute  of  latitude. 
On  the  parallel  of  60°  north  or  south  a  minute  of  longitude  is 
equal  to  only  half  a  minute  of  latitude.  Longitude  value  de- 
creases in  proceeding  from  the  equator  toward  the  poles,  where 
it  is  lost,  all  the  meridians  converging  to  a  point ;  consequently 
neither  the  north  nor  south  poles  possess  longitude. 

MINUTE  OF  ARC. — A  minute  of  angular  measure;  a 
minute  measured  on  the  sextant. 

MIRROR.  -  (See  Sextant.) 

MIXED  TRACK.— (See  Great-Circle  Sailing.) 

MOON. — An  opaque  celestial  body  receiving  its  light  from 
the  sun  ;  mean  distance  from  the  earth  238,800  miles  ;  diameter 
2,160  miles  ;  mean  apparent  diameter  32'. 

MOON  CULMINATING  STAR.— A  star  that  crosses  the 
meridian  at  the  same  time  that  the  moon  makes  its  transit. 

MORNING  STAR. — When  a  planet  rises  before  the  sun  it 
is  called  the  morning  star,  and  when  it  appears  in  the  western 
sky  shortly  after  sunset  it  is  called  the  evening  star. 

NADIR. — The  point  of  the  heavens  vertically  under  the  ob- 
server's feet.  The  nadir  is  diametrically  opposite  to  the  zenith. 


THE  NAVIGATOR'S  POCKET-BOOK  111 

NATIONAL  OBSERVATORY.— An  astronomical  estab- 
lishment situated  in  the  capital  city  of  a  nation.  The  meridian 
which  passes  through  the  observatory  is  accepted  as  the  first  or 
prime  meridian  of  that  country.  (See  Prime  Meridian.) 

NAUTICAL  ALMANAC.— (See  Almanac.) 

NAUTICAL  ASTRONOMY.— That  part  of  astronomy 
which  is  used  for  determining  the  latitude  and  longitude  of  the 
ship  by  calculations  of  the  sun,  moon,  and  stars.  Amplitudes 
and  azimuths  also  belong  to  nautical  astronomy. 

NAUTICAL  DAY.— Same  as  sea  day. 

NAUTICAL  MILE.— (See  Mile.) 

NAUTICAL  STARS.— Certain  bright  stars  tabulated  in  the 
Nautical  Almanac,  used  b}'  navigators  for  determining  the  ves- 
sel's position.  The  principal  ones  are  given  in  the  star  tables  in 
the  back  of  this  volume,  and  under  the  head  of  Fixed  Stars. 
(See  Latitude.) 

NAUTICAL  TABLES.— Specially  computed  tables  for  the 
solution  of  navigation  problems.  Bowditch's  tables,  published 
by  the  United  States  Government,  are  accepted  by  the  naval  au- 
thorities of  all  nations  as  standard,  although  England,  France, 
and  other  countries  have  their  own  tables.  Bowditch's  tables 
are  the  ones  referred  to  throughout  the  text  of  this  work. 

NAVIGATING  COMPASS.— The  standard  compass. 

NAVIGATION. — The  science  of  locating  the  position  of  a 
ship  at  sea,  and  conducting  a  vessel  from  one  port  to  another. 

NEUTRAL  POINT. — A  magnet  in  the  shape  of  a  steel  bat 
has  a  north  polarity  at  one  end  and  a  south  polarity  at  the  other. 
The  middle  of  the  bar  is  fairly  devoid  of  magnetism,  and  this 
space  is  called  the  neutral  point. 


112  THE  NAVIGATOR'S  POCKET-BOOK 

NOCTURNAL.— Relating  to  the  night. 

NOCTURNAL  ARC — The  arc  described  by  a  heavenly 
body  from  its  setting  to  its  rising. 

NODE. — When  a  planet  crosses  from  north  to  south  it  is  in 
the  descending  node,  and  when  it  crosses  from  south  to  north  it 
is  in  the  ascending  node. 

NOON. — When  the  centre  of  the  real  sun  is  on  the  observer's 
meridian  it  is  apparent  noon  not  only  with  him  but  at  all  places 
on  his  meridian  from  pole  to  pole.  (See  Mean  Sun ;  Siderial 
Noon.) 

OBJECT-GLASS.— The  lens  situated  in  the  large  end  of  a 
telescope,  the  same  being  the  first  to  receive  the  image  or  rays 
of  light. 

OBSERVATION. — To  determine  the  angular  height  of  a 
heavenly  body  above  the  horizon  for  the  purpose  of  calculating 
the  ship's  position. 

OCCULTATION. — The  eclipse  of  one  heavenly  body  by 
another. 

OCTANT. — A  nautical  instrument  of  reflection  for  measuring 
altitudes  of  heavenly  bodies.  It  is  constructed  on  the  same 
principles  as  the  sextant,  but  of  more  limited  arc  and  graduated 
to  only  15"  instead  of  10".  The  metal-frame  and  silver-arc  oc- 
tant with  an  arc  reading  to  about  120°  is  a  much  superior  instru- 
ment in  every  way  to  the  quadrant.  The  manner  of  adjusting 
and  using  the  octant  is  identical  with  that  of  the  sextant,  conse- 
quently it  would  be  repetition  to  treat  the  subject  under  this 
head,  and  the  reader  is  referred  to  the  rules  given  under  the 
head  of  Sextant.  Some  old-fashioned  octants  are  cut  to  20"  of 
arc  and  others  even  to  30".  (See  Quadrant ;  Sextant.) 


THE  NAVIGATOR'S  POCKET-BOOK  113 

OFF  THE  ARO.— (See  Sextant.) 

OIL  COMPASS.— A  liquid  compass ;  a  compass  in  which 
the  card  floats  about  in  oil  instead  of  a  mixture  of  alcohol  and 
water.  (See  Liquid  Compass.) 

ON  THE  ARC.— (See  Sextant.) 

OPPOSITION.— When  a  heavenly  body  is  180°  of  longitude 
distant  from  the  sun  it  is  said  to  be  in  opposition. 

ORBIT — The  imaginary  path  described  by  a  heavenly  body 
in  its  revolution  ;  the  track  of  a  planet  round  the  sun. 

P.M. — Post  Meridiem  ;  after  meridian  ;  embraces  the  twelve 
hours  from  noon  to  midnight. 

PARALLAX.— The  apparent  displacement  of  a  heavenly 
body  as  seen  from  two  different  stations.  The  sun's  parallax  is 
shown  in  Table  16  ;  the  moon's  parallax  (less  refraction)  in  Table 
23,  and  the  parallax  of  the  planets  in  Table  17.  (See  Corrected 
Altitude  ;  Horizontal  Parallax.) 

PARALLEL  RULES.— Two  flat  rules  connected  with  piv- 
oted cross-hinges  so  that  the  rules  may  remain  parallel  when 
spread  out.  They  are  used  for  shaping  courses  and  determining 
bearings  on  the  chart. 

PARALLELS.— Circles  of  latitude  parallel  to  the  equator. 

PARALLEL  SAILING.— Sailing  on  a  parallel ;  sailing  true 
east  and  west.  (See  Meridian  Sailing.) 

PARHELION.— A  mock  sun ;  an  image  of  the  sun  which 
is  occasionally  seen  close  to  and  at  the  same  height  above  the 
horizon  as  the  true  sun. 

PASSAGE.— (See  Meridian  Passage.) 

PATENT  LOG. — An  instrument  for  measuring  the  distance 
8 


114  THE  NAVIGATOR'S  DOCKET-BOOK 

(in  nautical  miles)  run  by  a  vessel.  It  consists  of  a  register, 
rotator,  and  line,  the  latter  connecting  the  two  metal  parts.  The 
rotator  is  towed  astern,  and  by  its  revolutions  turns  the  line  com- 
municating with  the  register  and  turns  the  dial  hands  within. 

To  Rig  the  Log. — Pass  the  log-line  through  the  long  fore-and- 
aft  hole  in  the  rotator  and  make  a  small  Flemish  eye  in  the  end  of 
the  line  ;  then  sew  a  piece  of  leather  for  chafing  gear  around  that 
part  of  the  line  which  rubs  against  the  small  or  forward  end  of 
the  rotator.  Next  secure  the  Flemish  eye  to  the  after-part  of  the 
rotator  by  the  wooden  or  metal  peg  furnished,  and  fasten  the 
hook  to  the  other  end  of  the  line  by  a  couple  of  half-hitches. 
Secure  the  indicator  so  that  it  will  ride  freely  on  the  taffrail, 
permitting  the  angle  of  the  indicator  bar  to  correspond  with  the 
angle  of  the  line,  thus  preventing  undue  friction  upon  the  shaft- 
bearing  when  the  log  is  being  towed.  Give  line  to  the  rotator 
according  to  the  freeboard  and  speed  of  the  vessel.  A  very  high 
freeboard,  or  a  steamer  making  more  than  ten  knots,  will  require 
all  the  line  furnished  to  prevent  the  rotator  from  skipping, 
whereas  a  low  freeboard  or  a  vessel  making  any wrhere  from  five 
to  ten  knots  will  require  about  two-thirds  of  the  line. 

To  Read  the  Dial. — Some  registers  have  two  and  some  three 
dials.  In  the  latter  case  the  first  one  is  marked  in  quarters,  each 
division  representing  one-quarter  of  a  mile  ;  the  second  in  even 
miles,  recording  as  high  as  ten  ;  the  third  in  ten-mile  divisions,  re- 
cording as  high  as  one  hundred.  When  the  ship  has  sailed  one 
hundred  miles,  the  three  hands  all  point  at  zero,  and  at  such 
time  a  suitable  memorandum  is  made  in  the  log-book,  so  that, 
the  record  may  be  faithfully  preserved.  Where  the  register  has 
only  two  dials,  one  of  them  represents  quarter  miles  and  the 
other  single-mile  divisions  extending  to  one  hundred. 

Remarks. — When  a  vessel's  speed  exceeds  eighteen  miles  an 


THE  NAVIGATOR'S  POCKET-BOOK  115 

hour,  the  majority  of  patent  logs  are  of  little  value,  as  they  will 
not  record  correctly  the  distance  run  by  the  vessel  on  account  of 
skipping.  If  sufficient  line  is  given  them  to  overcome  this  skip- 
ping and  attendant  loss,  they  will  be  too  sluggish  to  render  an 
honest  return.  In  such  cases  recourse  is  had  to  the  chip  log, 
and  the  rough  distance  run  is  also  calculated  by  dividing  the 
number  of  revolutions  made  by  the  propeller  by  the  number 
allowed  for  one  mile. 

To  Allow  for  Current. — When  a  ship  is  sailing  with  or  against 
a  current,  the  velocity  of  same  must  be  taken  into  account  and 
applied  either  as  a  plus  or  minus  quantity  to  the  reading  of  the 
dial. 

Examples. — According  to  the  register,  the  vessel  heading  west 
has  made  ten  miles  in  the  past  hour,  but  it  is  known  that  during 
that  time  the  ship  has  been  in  a  current  flowing  west  at  the  rate 
of  two  miles  an  hour  ;  consequently  this  two  miles  must  be  added 
to  the  reading  of  the  register,  making  the  corrected  distance  run 
twelve  miles. 

The  register  shows  that  during  the  past  hour  the  vessel  head- 
ing south  has  made  ten  miles,  but  it  is  known  that  during 
that  time  the  ship  has  been  in  a  current  setting  north  at 
the  rate  of  two  miles  an  hour  ;  consequently  this  two  miles  must 
be  subtracted  from  the  reading  of  the  register,  making  the  cor- 
rected distance  run  only  eight  miles. 

*  Explanation. — When  a  vessel  is  going  neither  directly  with 
or  against  a  current,  but  sailing  a  course  that  makes  an  angle 
with  it,  then  it  becomes  a  calculation  of  current  sailing,  and 
must  be  considered  in  the  manner  explained  under  that  head. 

PATTERSON'S  METHOD.— (See  Chart  Sailing.) 
PELORUS. — An  instrument  much  used  for  observing  bear- 


116  THE  NAVIGATOR'S  -POCKET-BOOK 

ings  and  for  finding  the  deviation  of  the  compass,  taking  the 
place  of  the  azimuth  attachment,  shadow-pin,  etc.  It  consists  of 
a  circular  dial  of  brass  graduated  with  the  points  and  degrees  of 
the  compass,  and  two  upright  arms  which  revolve  around  the 
circle.  This  plate  is  hung  in  gimbals  so  that  it  will  preserve  a 
horizontal  position  when  the  vessel  pitches  and  rolls.  One  of  the 
uprights  is  fitted  with  a  perpendicular  thread  running  its  length, 
also  a  small  hinged  mirror  at  its  base,  and  the  other  upright  is 
provided  with  a  colored  eye-screen  which  is  made  to  slide  up 
and  dowrn  the  length  of  the  arm,  and  is  for  the  purpose  of  pro- 
tecting the  eye  from  the  glare  of  the  sun  wrhen  taking  a  bearing 
of  that  body.  A  mark  on  the  inner  gimbal  ring  indicates  the 
line  of  the  keel  or  the  ship's  head,  and  a  clamp  screw  admits  of 
the  dial  being  secured  against  turning  after  it  has  been  set. 

Pelorus  Stands. — Suitable  stands  for  the  pelorus  should  be 
provided  on  different  parts  of  the  deck,  in  order  that  bearings 
may  be  taken  at  any  station  by  simply  carrying  the  pelorus  to  it 
and  setting  it  on  its  stand.  The  idea  of  this  is  that  if  the  view  is 
obstructed  (by  a  mast,  funnel,  sail,  or  deck-house)  from  one 
point,  another  may  be  selected  which  will  give  a  clear  field.  It 
is  recommended  that  steamships  have  stands  built  on  each  end 
of  the  bridge  and  on  each  quarter.  These  stands  require  to  be 
but  simple  shelves  hinged  to  the  rail  and  provided  with  raised 
strips  or  coamings  of  wood  running  round  them  for  the  pelorus 
box  to  snugly  set  into  and  to  protect  the  same  from  rolling  off. 
The  stands  must  have  their  fore-and-aft  coamings  parallel  to  the 
ship's  keel,  so  that  when  the  pelorus  box  is  placed,  the  zero  line 
of  the  card  will  coincide  with  the  line  of  the  keel.  The  man- 
ner of  effecting  this  is  explained  in  the  following  : 

The  ship  being  on  an  even  keel  while  in  dock  or  at  anchor  in 
the  stream,  set  the  pelorus  square  on  one  of  the  shelves,  with  the 


THE  NAVIGATOR'S  POCKET-BOOK  117 

lubber's  mark  forward,  and  measure  carefully  the  distance  from 
the  centre  of  the  instrument  to  the  midship  seam  of  the  deck, 
then  lay  off  toward  the  bulwarks  from  this  seam  a  conspicuous 
mark  on  the  forward  deck  (on  the  side  that  the  instrument  is  on) 
the  same  distance  as  exists  between  the  pelorus  and  the  seam. 
Next  set  the  zero  point  of  the  pelorus  dial  to  the  lubber's  mark 
on  the  gimbal  ring,  and  observe  that  the  sight- vanes  are  placed  at 
zero.  Look  forward  through  the  sight- vanes  at  the  mark  erected, 
and  move  the  box  one  way  or  the  other  until  the  mark  is  seen 
to  be  cut  by  the  thread.  Now  secure  the  coamings  on  the  lines 
indicated  by  the  box,  and  proceed  in  a  like  manner  for  each  one 
of  the  shelves. 

To  Take  a  Bearing. — Set  the  pelorus  to  the  course  of  the 
ship  according  to  the  standard  or  navigating  compass,  then  so 
long  as  the  ship  is  held  steady  on  said  course,  any  bearings  taken 
by  the  pelorus  will  represent  the  magnetic  bearing  of  the  object 
exactly  the  same  as  though  it  had  been  observed  directly  from 
the  standard  compass  itself. 

In  order  to  find  the  deviation  of  any  particular  compass,  simply 
set  the  pelorus  to  the  course  of  the  ship  as  shown  by  that  com- 
pass, and  proceed  to  take  the  sun's  bearing  and  work  out  the  am- 
plitude or  azimuth.  (See  Amplitude  ;  Azimuth.) 

PERMANENT  MAGNETISM.— An  artificial  steel  magnet 
will  part  with  a  little  of  its  original  strength  after  being  charged, 
the  balance  constituting  what  is  known  as  its  saturation  point, 
which  it  will  retain  for  many  years  without  appreciable  loss, 
and  is  known  as  permanent  magnetism. 

PERPENDICULAR.— A  line  at  right  angles  to  the  plane  of 
the  horizon  ;  a  plumb-line  ;  a  line  at  a  right  angle  to  the  base. 

PERSONAL   EQUATION.— The  difference  in  judgment 


118  THE  NAVIGATOR'S  POCKET-BOOK 

shown  between  two  observers  in  measuring  an  altitude  of  the 
same  object,  etc. 

PLANE. — A  level  surface.  In  astronomy  planes  are  ideal 
and  pass  through  certain  points  of  the  heavens — planes  of  the 
horizon,  equator,  etc. 

PLANE  CHART. — A  chart  representing  the  earth's  surface 
as  a  plane. 

PLANE  SAILING. — Calculating  courses,  etc.,  on  the  sup- 
position that  the  surface  of  the  earth  is  a  plane. 

PLANET. — An  opaque  celestial  body,  which,  like  the  moon, 
receives  its  light  from  the  sun.  The  nine  principal  planets  are 
Mercury,  Venus,  Earth,  Moon,  Mars,  Jupiter,  Saturn,  Uranus, 
Neptune.  (See  Fixed  Stars.) 

PLANISPHERE.— A  chart  of  the  heavens. 

PLOTTING. — To  plot  the  latitude  and  longitude  of  a  vessel 
is  to  trace  on  a  chart  the  courses  and  distances  made.  Where 
the  last  line  ends  will  be  the  ship's  place.  It  is  a  modification  of 
dead-reckoning. 

POINT. — One  of  the  thirty-two  divisions  of  the  compass  card  ; 
exact  place ;  station. 

POINTERS.— The  two  stars  in  the  ladle  of  the  Dipper  that 
point  out  the  North  Star.  (See  Dipper.) 

POLAR  CIRCLES.— The  two  parallels  situated  23°  28'  from 
the  poles  of  the  earth.  (See  Antarctic  Circle  ;  Arctic  Circle.) 

POLAR  DISTANCE. — The  angular  distance  of  a  heavenly 
body  from  the  elevated  pole,  the  same  being  found  by  either 
adding  its  declination  to  or  subtracting  it  from  90°.  Polar  dis- 
tance is  reckoned  from  the  pole  that  is  in  the  hemisphere  of  the 
observer.  For  example,  if  the  observer  is  in  north  latitudes,  the 


THE  NAVIGATOR'S  POCKET-BOOK  119 

angular  distance  of  the  body  would  be  figured  from  the  ele- 
vated north  pole,  and  if  the  observer  was  in  the  southern  hemi- 
sphere, it  would  be  measured  from  the  south  pole. 

Examples. — An  observer  situated  north  of  the  equator  wishes 
to  know  the  sun's  polar  distance.  The  declination  of  the  body 
is  10°  north  ;  consequently  the  sun's  north  polar  distance  is  80°. 

An  observer  situated  south  of  the  equator  requires  the  moon's 
polar  distance.  The  declination  of  the  body  is  20°  north  ;  con- 
sequently the  moon's  south  polar  distance  is  110°. 

POLARIS. — The  Pole  or  North  Star.  It  is  a  star  of  the  sec- 
ond magnitude  in  the  tail  of  the  Little  Bear.  Polaris  is  only 
about  1  J°  from  the  pole,  and  its  altitude  is  always  the  approxi- 
mate latitude  of  the  observer.  When  Polaris  is  at  its  greatest 
distance  from  the  meridian  its  altitude  is  practically  the  same  as 
the  elevation  of  the  pole,  which  is  equal  to  the  latitude  of  the  ob- 
server. Polaris  is  calculated  to  be  many,  many  hundreds  of 
millions  of  miles  from  the  earth.  Polaris  is  approaching  the 
pole,  and  in  a  hundred  and  twenty  years  from  now  it  will  be 
about  30'  from  it,  after  which  it  will  commence  to  recede.  These 
changes  arise  from  the  precession  of  the  equinoxes.  The  annual 
variation  of  the  declination  of  Polaris  is  19"  ;  in  other  words, 
it  is  approaching  the  pole  at  the  rate  of  19"  yearly. 

POLE  COMPASS. — A  compass  that  is  elevated  above  the 
deck  by  means  of  a  long,  stout  pole.  Access  is  had  to  the  in- 
strument by  a  ladder  fixed  permanently  between  the  deck  and 
the  top  of  the  pole.  The  compass  is  so  situated  to  remove  it 
beyond  the  disturbing  influences  of  the  ship's  iron. 

POLES. — The  extremities  of  the  earth's  axis  ;  the  two  points 
on  the  earth's  surface  90°  distant  from  the  equator.  (See  Mag- 
netic Poles.) 


120  THE  NAVIGATOR'S  POCKET-BOOK 

POSITION. — Relating  to  the  place  of  the  ship. 

PRECESSION  OF  THE  EQUINOXES.— The  equinoctial 
points  do  not  preserve  a  constant  place  among  the  stars,  but 
move  backward,  or  toward  the  west,  along  the  ecliptic  at  the 
annual  rate  of  50";  consequently  a  complete  revolution  occu- 
pies 25,868  years.  The  precession  is  caused  by  the  unequal  at- 
traction of  the  sun  and  moon  on  the  equator,  combined  with  the 
earth's  rotation  on  its  axis. 

PRICKING  POSITION.— With  the  dividers  take  from  the 
graduated  meridian  on  the  side  of  the  chart  the  given  latitude 
and  mark  this  on  the  meridian  the  nearest  to  the  given  longitude  ; 
then  lay  the  bevelled  edge  of  the  parallel  rules  on  a  near  parallel 
and  slide  them  along  to  the  point  marked  on  the  meridian.  Now 
with  the  dividers  take  the  given  longitude  from  the  graduated 
parallel  and  lay  this  down  along  the  edge  of  the  parallel  rules, 
and  this  will  define  the  ship's  latitude  and  longitude. 

PRIMARY  MERIDIAN — Same  as  Prime  Meridian. 

PRIME  MERIDIAN.— The  starting-point  of  longitude. 
The  first  meridian  of  a  country  established  by  the  situation  of  its 
national  observatory.  Longitude  is  counted  east  and  west  from 
the  first  meridian  up  to  180°.  The  French  use  the  meridian  of 
Paris  as  a  first  meridian  ;  the  English  that  of  Greenwich  ;  the 
Russians  that  of  St.  Petersburg  ;  the  Americans  that  of  Wash- 
ington, etc.  For  convenience,  American  navigators  (and  others) 
also  use  the  meridian  of  Greenwich,  as  it  permits  them  to  navi- 
gate by  English  charts,  many  of  the  same  representing  parts  of 
the  world  of  which  we  have  no  survey  of  our  own.  For  pur- 
poses of  navigation,  a  chronometer  must  be  regulated  to  the 
prime  meridian  of  the  country  whose  chart  is  used— if  a  French 
chart  is  employed,  the  chronometer  must  be  set  to  Paris  time ; 


THE  NAVIGATOR'S  POCKET-BOOK  121 

if  an  English  chart  is  used,  the  chronometer  must  represent 
Greenwich  time,  etc.  (See  Circumnavigator's  Day  ;  Secondary 
Meridians.) 

PRIME  VERTICAL. — The  vertical  circle  passing  through 
the  east  and  west  points  of  the  horizon.  A  heavenly  body  is  in 
or  on  the  prime  vertical  when  it  bears  true  east  or  true  west — 
when  it  is  at  right  angles  to  the  meridian.  When  a  body  is  ob- 
served on  the  prime  vertical  for  the  purpose  of  calculating  the 
longitude,  a  considerable  error  in  the  latitude  by  dead-reckon- 
ing (used  in  the  computation)  will  not  appreciably  affect  the  re- 
sult. By  this  it  will  be  understood  that  the  best  time  to  observe 
a  longitude  sight  (be  it  sun,  moon,  planet,  or  star)  is  when  the 
body  is  on  the  prime  vertical  ;  but  it  is  to  be  explained  that  it 
is  not  always  possible  to  obtain  such  an  observation,  for  a  heav- 
enly body  can  only  bear  true  east  or  true  west  when  its  declina- 
tion is  of  the  same  name  as  the  ship's  latitude  and  less  than  the 
latter.  When  the  declination  of  the  body  is  of  the  same  name 
but  greater  than  the  ship's  latitude,  the  body's  nearest  approach 
to  the  prime  vertical  will  be  some  time  after  it  has  risen ;  but 
when  the  declination  is  of  a  contrary  name  to  the  latitude,  the 
body  will  be  the  nearest  to  the  prime  vertical  at  its  rising  and 
setting.  By  referring  to  a  set  of  azimuth  tables  the  navigator 
will  be  able  by  mere  inspection  to  determine  the  hour  and  min- 
ute that  the  body  will  be  on  or  will  approach  the  nearest  to  the 
prime  vertical.  All  that  is  necessary  is  to  refer  to  the  page  show- 
ing the  ship's  latitude  and  the  declination,  then  run  down  the 
latter  column  until  the  closest  figures  to  90°  are  obtained,  and 
look  opposite  in  the  side  column  for  the  time.  When  the  dec- 
lination and  the  latitude  are  nearly  the  same,  the  sun  will  be 
nearest  the  prime  vertical  a  short  time  before  and  after  its  inerid- 


122  THE  NAVIGATOR'S  POCKET-BOOK 

ian  passage,  consequently  at  such  times  a  very  high  altitude 
may  be  employed  for  finding  the  longitude  of  the  ship. 

PRISMATIC  ATTACHMENT — A  small  portable  instru- 
ment fitted  with  a  prism-glass,  so  adjusted  on  top  of  the  com- 
pass glass  that  the  bearing  of  an  object  may  be  read  from  the 
compass  card  by  reflection. 

PROJECTIONS. — Charts  ;  maps  ;  delineations. 

PROTRACTOR.  —  An  instrument  for  measuring  angles. 
(See  Course  Protractor.) 

QUADRANT. — A  navigating  instrument  of  reflection  used 
for  measuring  angles.  It  is  on  the  same  principle  as  the  octant 
and  sextant,  but  inferior  in  construction  and  graduated  only  to 
1'  of  arc. 

Description  of  the  Quadrant. — The  quadrant  contains  an  arc 
of  45°,  but  owing  to  its  double  reflection  it  measures  90°,  read- 
ing from  right  to  left.  The  arc  is  divided  into  degrees,  and 
these  are  subdivided  into  three  parts  of  twenty  minutes  each, 
and  the  vernier  on  the  sliding  limb  is  divided  into  single  min- 
utes. The  sliding  or  index  limb  is  moved  from  right  to  left  in 
measuring  altitudes,  and  the  screw  on  the  back  is  used  for 
clamping  it  against  the  arc  after  the  altitude  has  been  roughly 
measured.  The  screw  on  the  forward  part  of  the  limb  is  called 
the  tangent  screw  (set  tangent  to  the  arc)  and  is  used  for  gently 
moving  the  sliding  limb  when  it  is  clamped  so  as  to  make  a 
perfect  contact  of  the  body  with  the  horizon.  The  colored 
glasses  are  for  shading  the  eye  when  obtaining  an  altitude  of 
the  sun. 

To  Read  the  Altitude — Ascertain  the  number  of  degrees  and 
thirds  of  a  degree  that  the  zero  on  the  vernier  has  passed  on  the 
arc,  then  look  along  the  vernier  until  one  of  its  lines  cuts  ex- 


THE  NAVIGATOR'S  POCKET-BOOK  123 

actly  with  one  of  the  lines  on  the  arc,  and  the  number  of  min- 
utes given  on  the  vernier  will  be  added  to  the  reading  originally 
obtained  on  the  arc — the  whole  answer  being  the  required  alti- 
tude. 

Remarks. — The  quadrant  is  a  crude  instrument,  and  is  not 
used  by  good  navigators.  The  metal-frame  octant  and  the  sex- 
tant are  standard  instruments,  but  on  account  of  the  sextant 
affording  means  of  measuring  greater  angles  than  the  former,  it 
is  to  be  preferred  to  the  octant. 

The  quadrant  is  adjusted  in  the  same  manner  as  explained  for 
the  sextant.  (See  Octant;  Sextant.) 

QUADRANTAL  DEVIATION.— The  deviation  of  the  com- 
pass  arising  from  the  effects  of  the  induced  magnetism  in  thwart- 
ships  and  fore-and-aft  iron  in  the  ship,  and  which  is  corrected 
by  two  iron  spheres  attached  to  the  port  and  starboard  sides 
of  the  binnacle.  These  spheres  are  known  as  quadrantal  cor- 
rectors. 

QUADRATURE.— When  the  moon  is  90°  from  the  sun— at 
one  of  the  two  points  in  her  orbit  equally  distant  from  the  con- 
junction and  opposition — she  is  said  to  be  in  quadrature. 

RADIUS. — The  distance  from  the  centre  of  a  circle  to  its  cir- 
cumference. 

RATE. — The  daily  variation  of  a  chronometer  from  the  time 
of  the  meridian  to  which  it  is  set.  The  aggregate  of  the  gain  or 
loss  is  respectively  subtracted  from  or  added  to  the  face  of  the 
chronometer  in  order  to  obtain  the  correct  Greenwich  mean  time 
at  the  instant  of  observation. 

Sea  Rate.— Sometimes  the  chronometer  does  not  maintain 
when  at  sea  the  rate  furnished  for  it  by  the  makers  or  dealers, 
and  which  is  known  as  the  instrument's  shore  rate.  To  as- 


124  THE  NAVIGATOR'S  POCKET-BOOK 

certain  the  sea  rate,  take  the  difference  between  the  chronom- 
eter's  error  on  the  day  of  sailing  and  the  gross  error  deter- 
mined when  the  vessel  makes  port,  and  the  result  divided  by 
the  number  of  days  at  sea  will  be  the  sea  rate.  (See  Chronom- 
eter.) 

RATIONAL  HORIZON.— -A  plane  passing  through  the  cen- 
tre of  the  earth  and  parallel  to  the  sensible  horizon  at  the  ob- 
server's station.  (See  Sensible  Horizon.) 

READING.— To  read  an  altitude  is  to  observe  the  height  of 
an  object  recorded  on  the  arc  of  a  sextant,  octant,  etc. 

RECIPROCAL  BEARINGS. — Mutual  bearings  of  the  same 
object  by  two  compasses  placed  in  line,  one  on  board  and  the 
other  on  shore  where  it  is  free  from  magnetic  disturbances  in 
the  way  of  local  attraction. 

REDUCTION.— To  change  hours,  minutes,  and  seconds  into 
arc,  or  to  change  degrees  into  time.  To  apply  a  certain  quan- 
tity of  arc  to  an  ex-meridian  altitude  is  called  reduction  to  the 
meridian. 

REFRACTION. — The  change  of  direction  of  a  ray  of  light 
in  passing  through  atmospheric  mediums  of  varying  density. 
Refraction  is  ever  a  minus  correction,  and  is  tabulated  in  Table 
20  for  all  heavenly  bodies.  It  is  to  be  explained,  however,  that 
Table  23  gives  the  parallax  of  the  moon,  less  the  refraction.  (See 
Corrected  Altitude.) 

REGULATING. — What  is  known  as  regulating  a  watch  or 
clock  at  sea  is  simply  to  correct  it  so  that  it  will  show  the  local 
apparent  time  at  ship.  It  is  done  as  follows  :  Observe  an  alti- 
tude of  the  sun  as  for  a  regular  chronometer  sight  for  finding 
longitude,  and  also  note  the  time  shown  by  the  ship's  clock  at 


THE  NAVIGATOR'S  POCKET-BOOK  125 

the  instant ;  then  proceed  to  work  up  the  sight  by  the  regular 
rule  (see  Longitude),  and  compare  the  apparent  time  at  ship 
given  for  the  sine  of  the  logarithms  with  the  time  shown  by  the 
clock  when  the  sight  was  taken  ;  the  difference  will  be  the  error 
of  the  clock,  the  hands  of  which  will  be  set  back  or  advanced 
as  required.  This  method  is  also  known  as  finding  the  time. 

RESIDUAL  ERRORS. — Deviation  remaining  after  the  com- 
pass has  been  adjusted  as  closely  as  possible.  (See  Compass.) 

RETENTIVE  MAGNETISM.— When  a  ship's  head  has 
been  in  one  direction  for  a  long  time  either  at  a  dock  or  on  a 
long  course  at  sea,  the  hull  becomes  temporarily  magnetized  in 
a  direction  parallel  to  the  magnetic  meridian,  owing  to  the 
earth's  inductive  force.  Sometimes  this  magnetism  remains  for 
several  hours  after  the  direction  of  the  ship's  head  has  been 
changed,  hence  its  name  "retentive."  It  then  gives  way  to 
magnetism  induced  in  a  new  direction  according  to  the  change 
of  course.  It  is  because  of  this  retentive  magnetism  that  the 
deviation  card  should  be  continually  checked  at  sea,  especially 
upon  changing  the  course.  The  temporary  effect  of  retentive 
magnetism  upon  the  compass  is  to  cause  it  to  deviate  invariably 
in  the  direction  of  the  last  course,  hence  if  a  vessel  has  been 
heading  south  for  several  days,  and  her  course  is  changed  to 
west,  it  will  be  found  that  the  natural  deviation  for  that  point 
has  been  increased  if  the  deviation  has  been  westerly,  and  dimin- 
ished if  it  has  been  easterly. 

REVOLVING  STORM.— (See  Law  of  Storms.) 

RHUMB  LINE.— The  track  of  a  ship  sailing  constantly 
toward  the  same  point  of  the  compass ;  a  line  prolonged  on  a 
nautical  chart  from  any  point  of  the  diagram  compass. 

RIGHT  ASCENSION. — The  distance  considered  in  time  of 


126  THE  NAVIGATOR'S  POCKET-BOOK 

a  heavenly  body  reckoned  eastward  on  the  equinoctial  from  the 
First  Point  of  Aries— counted  from  0  h.  to  24  h.  (0°  to  360°). 
The  First  Point  of  Aries  is  that  point  in  the  heavens  which  the 
sun's  centre  occupies  at  the  time  of  the  vernal  equinox,  when 
the  body  changes  from  south  to  north  declinations.  Right  as- 
cension may  be  expressed  as  the  celestial  longitude  of  a  heaven- 
ly body.  The  correction  for  the  hourly  or  minute  difference  of 
right  ascension  is  found  and  applied  in  the  same  way  as  explained 
for  the  difference  of  declination.  In  other  words,  the  right  as- 
cension is  reduced  to  the  Greenwich  time  of  observation  as 
shown  by  the  chronometer,  by  multiplying  the  hourly  difference 
in  the  case  of  the  sun  and  planets,  but  the  minute  difference  in 
the  case  of  the  moon,  and  then  adding  this  correction  to  or  sub- 
tracting it  from  the  right  ascension  proper  according  as  the  lat- 
ter is  increasing  or  decreasing. 

RIGHT  ASCENSION  OF  THE  MERIDIAN.— The  angle 
at  the  pole  included  between  the  meridian  of  the  observer  and 
the  meridian  passing  through  the  First  Point  of  Aries.  It  is 
reckoned  eastward  in  the  order  of  the  signs.  Sidereal  time  and 
right  ascension  of  the  meridian  are  one  and  the  same  thing.  In 
other  words,  the  hour  angle  of  the  First  Point  of  Aries  is  equal 
to  the  right  ascension  of  the  meridian  of  an  observer,  which  is 
precisely  the  same  thing  as  sidereal  time. 

RIGOROUS  METHOD. — Navigation  problems  calculated 
according  to  exact  principle  ;  allowing  of  no  abatement ;  accu- 
rate in  the  smallest  detail. 

RISING.— The  appearance  of  a  heavenly  body  mounting 
above  the  horizon.  Celestial  bodies  continue  to  rise  from  the 
eastern  horizon  line  until  they  cross  the  meridian  of  the  observ- 
er, when  they  begin  to  fall. 


THE  NAVIGATOR'S  POCKET-BOOK  127 

ROUGH  LOG.— Same  as  log  slate. 

SAILINGS — (See  Great-Circle,  Mercator's,  Meridian,  Mid- 
dle-Latitude, Parallel,  Plane,  and  Spherical  Sailings.) 

SATURATION  POINT.— (See  Permanent  Magnetism.) 

SEA  DAY. — The  old  fashioned  way  of  keeping  the  date  at 
sea  was  to  consider  the  day  and  date  to  commence  at  noon  and 
to  end  and  begin  again  the  following  noon,  so  that  the  sea  day 
and  date  began  twelve  hours  before  the  civil  date  and  twenty- 
four  hours  before  the  astronomical  date.  This  ridiculous  prac- 
tice belongs  entirely  to  the  past. 

SEA  RATE.— (See  Rate.) 

SECONDARY  MERIDIANS — Those  connected  with  the 
prime  meridian  by  exchange  of  telegraphic  time  signals.  Sec- 
ondary meridians  are  determined  with  the  utmost  degree  of  care 
in  order  to  locate  with  accuracy  the  positions  of  prominent 
points  on  the  coasts.  (See  Tertiary  Meridians.) 

SEMICIRCULAR  DEVIATION.— So  called  because  it  has 
the  contrary  name  and  maximum  value  in  opposite  semicircles  ; 
for  instance,  if  it  is  westerly  on  north  it  will  be  easterly  on  south. 

SEMIDIAMETER.— Half  a  diameter.  The  semidiameters 
of  the  sun  and  moon  are  given  in  the  Nautical  Almanac  for  every 
day  of  the  year,  but  for  purposes  of  practical  navigation  these 
may  be  called  16'.  (See  Corrected  Altitude.) 

SEND  OF  THE  SEA — (See  Heave  of  the  Sea.) 

SENSIBLE  HORIZON.— A  plane  which  is  tangent  to  the 
surface  of  the  earth  where  the  observer  is  situated.  This  plane 
extends  north,  south,  east,  and  west  until  bounded  by  the  sky. 
(See  Visible  Horizon.) 

SET. — A  heavenly  body  sets  when  its  upper  limb  dips  below 


128  THE  NAVIGATOR'S  .POCKET-BOOK 

the  horizon  line  ,  an  altitude  is  set  when  the  sliding  limb  of  the 
sextant  is  clamped  against  the  arc ;  the  space  (span)  contained 
between  the  points  of  the  dividers  in  measuring  a  distance  on 
the  chart  is  known  as  a  set ;  to  set  the  ship's  course  is  to  com- 
mence steering  in  the  calculated  direction  ;  the  set  of  a  current 
is  the  direction  of  its  flow. 

SEXTANT.— An  instrument  of  reflection  used  by  navigators 
for  measuring  the  altitudes  of  heavenly  bodies,  and  for  observ- 
ing angles.  It  is  of  more  delicate  mechanism  than  the  quadrant 
or  octant,  and  where  the  former  is  graduated  (or  cut,  as  it  is 
often  called)  to  minutes,  and  the  latter  to  15"  of  arc,  the  sextant 
reads  to  10".  The  engraving  in  the  front  of  the  book  represents 
the  navigator's  sextant. 

Names  of  Various  Parts. — A,  the  graduated  arc  ;  the  divi- 
sions of  the  arc  are  10'  each,  and  these  are  subdivided  by  the 
vernier  to  10";  H,  the  handle,  by  which  the  sextant  is  held  i. 
the  right  hand  ;  M,  the  mirror,  or  index-glass,  at  the  end  of  th e 
sliding  limb  ;  m,  the  horizon-glass  ;  E,  the  magnifying  telescope 
for  giving  greater  distinctness  to  the  images,  is  placed  in  the 
line  of  sight  and  supported  in  the  ring  or  collar,  K,  which  ca1 
be  moved  by  a  screw  at  the  back  in  a  direction  at  right  angles  to 
the  plane  of  the  sextant,  so  that  the  axis  of  the  telescope  may  be 
directed  either  toward  the  silvered  or  transparent  part  of  the 
horizon-glass  ;  the  vernier  is  read  by  means  of  the  magnifying- 
glass,  R,  attached  to  a  revolving  arm,  S,  which  is  secured  upOL 
the  index  bar  or  sliding  limb  ;  P  and  Q,  the  colored  shade- 
glasses,  for  shielding  the  eye  from  the  glare  of  the  sun  ;  P,  the 
shades  through  which  the  image  of  the  sun  passes  from  the  mir- 
ror to  the  horizon-glass  ;  Q,  the  back  shade-glasses  for  protect- 
ing the  eye  from  the  glare  of  the  horizon  showing  through  the 
unsilvered  part  of  the  horizon-glass  ;  B,  the  tangent  screw  (set 


THE  NAVIGATOR'S  POCKET-BOOK  129 

tangent  to  the  plane  of  the  instrument)  by  which  the  vernier  may 
be  moved  delicately  along  the  arc  after  the  sliding  limb  has  been 
clamped  by  the  screw  C  at  the  back  ;  I,  the  inverting  telescope  ; 
F,  the  simple  tube  without  glasses  for  giving  a  direct  line  of 
sight  from  the  centre  of  the  telescope  ring  to  the  horizon-glass. 

The  inverting  telescope,  with  its  parallel  wires,  is  principally 
used  for  measuring  angular  distances  of  heavenly  bodies — a 
branch  of  nautical  astronomy  that  does  not  come  within  the 
limits  of  this  work.  Altitudes  may  be  measured  by  it  in  place 
of  either  of  the  other  telescopes,  but  it  requires  considerable 
practice  and  a  very  steady  hand.  As  its  name  implies,  objects 
viewed  through  it  appear  upside  down,  so  that  to  measure  an 
altitude  by  it  the  navigator  would  bring  the  horizon  down  to  the 
sun,  instead  of  the  sun  down  to  the  horizon. 

The  small  key  shown  is  for  adjusting  the  horizon-glass,  and 
the  small  ring  beside  it  contains  a  colored  glass,  and  this  may  be 
screwed  on  the  eye  end  of  the  telescopes  as  a  substitute  for  the 
shade-glasses. 

The  star  telescope  contributes  illuminating  power  to  an  obser- 
vation owing  to  its  short  tube  and  large  object-glass,  and  permits 
the  navigator  to  see  the  horizon  distinctly  when  otherwise  it 
would  be  obscured.  If  not  provided  with  this  valuable  adjunct 
the  navigator  should  have  one  fitted  to  his  sextant,  and  be  partic- 
ular that  its  collimation  adjustment  is  made  perfect. 

Adjustment  of  the  Index-Glass. — This  glass  must  be  per- 
pendicular to  the  plane  of  the  sextant  To  prove  this,  set  the 
vernier  to  about  the  centre  of  the  arc  and  clamp  it,  then  look 
obliquely  into  the  index-glass  and  observe  if  the  arc  seen  direct 
and  its  reflection  form  one  continuous  line  ;  if  so,  the  glass  is 
perpendicular  to  the  plane  of  the  instrument,  but  if  the  reflected 
image  appears  to  be  lower  than  the  other  it  proves  that  the  glass 
9 


130  THE  NAVIGATOR'S. POCKET-BOOK 

leans  backward  ;  if,  however,  the  reflected  image  appears  to  be 
higher  than  the  other  the  glass  leans  forward. 

Adjustment  of  the  Horizon-Glass. — This  glass  must  also  be 
perpendicular  to  the  plane  of  the  sextant.  To  test  this,  let  zero 
on  the  vernier  cut  zero  on  the  arc,  and  hold  the  instrument  al- 
most horizontal,  noting  if  the  direct  and  reflected  images  of  the 
horizon  line  coincide — that  is,  if  they  show  as  an  unbroken  line 
both  in  the  silvered  and  clear  parts  of  the  glass.  If  they  do,  the 
horizon-glass  is  perpendicular,  but  if  they  do  not,  then  adjust 
the  glass  to  the  required  angle  by  the  adjusting  screw. 

The  Two  Glasses  to  Be  Parallel.— With  the  two  zeros  cut- 
ting, hold  the  instrument  vertically,  and  if  the  direct  and 
reflected  images  of  the  horizon  line  show  as  an  unbroken  and 
continuous  line  the  horizon-glass  is  parallel  to  the  index-glass, 
but  if  they  do  not  show  in  an  unbroken  line  adjust  the  horizon- 
glass  by  its  adjusting  screw. 

To  Find  the  Index  Error.— Should  it  prove  impossible  to 
obtain  a  perfect  adjustment  find  the  error  of  the  instrument  as 
follows :  let  the  two  zeros  cut,  then  holding  the  instrument 
vertically  look  at  the  horizon  and  gently  finger  the  tangent 
.jscrew  so  as  to  move  the  vernier  either  forward  or  backward  along 
the  arc  until  the  image  of  and  the  horizon  line  itself  show  in  an 
unbroken  line  across  the  glass  ;  then  the  difference  between  zero 
on  the  vernier  and  zero  on  the  arc  will  be  the  index  error,  and 
the  amount  of  same  will  be  added  to  any  altitude  observed  by 
the  instrument  if  zero  on  the  vernier  is  to  the  right  hand  (off  the 
arc)  of  zero  on  the  arc,  but  the  amount  will  be  subtracted  if 
zero  on  the  vernier  is  to  the  left  hand  (on  the  arc)  of  zero  on 
the  arc. 

Telescope  Adjustment.— Screw  in  the  telescope  containing 
the  two  parallel  wires  and  see  that  they  are  turned  until  parallel 


THE  XAVIGATOK'S  POCKET-BOOK  131 

with  the  plane  of  the  sextant  ;  then  select  two  stars,  at  least  90° 
apart,  and  make  an  exact  contact  at  the  wire  nearest  the  plane 
of  the  instrument,  and  read  the  measured  angle.  Move  the 
sextant  so  as  to  throw  the  objects  on  the  other  wire,  and  if  the 
contact  is  still  perfect  the  axis  of  the  telescope  is  in  its  right  situ- 
ation and  the  telescope  adjustment  is  correct.  If  the  images 
have  separated  it  shows  that  the  object  end  of  the  telescope 
droops  toward  the  plane  of  the  sextant,  and  if  the  images  over- 
lap it  proves  that  the  object  end  of  the  telescope  points  away 
from  the  plane  of  the  instrument.  This  will  be  rectified  by  the 
screws  in  the  collar  of  the  sextant.  A  defect  in  the  telescope 
adjustment  always  makes  angles  too  great.  (See  Axis  of  Col- 
limation.) 

Tormenting  a  Sextant. — The  author  desires  to  caution 
navigators  against  tormenting  a  sextant  continually.  A  good 
instrument  once  placed  in  perfect  adjustment  (unless  it  meets 
with  a  heavy  jar  or  fall)  will  keep  in  adjustment  for  a  long  time, 
and  if  let  alone  will  give  more  satisfactory  work  than  if  the 
threads  of  the  adjusting  screws  have  become  loose  and  worn 
from  incessant  slacking  and  setting  up. 

To  Read  the  Sextant  Altitude. — Ascertain  by  looking  toward 
the  left  how  many  degrees  and  ten-minute  divisions  the  vernier 
zero  has  passed  on  the  arc,  then  look  along  the  vernier  to  the  left 
until  one  of  its  lines  coincides  exactly  with  one  of  the  lines  of  the 
arc,  and  the  number  of  vernier  minutes  and  ten-second  divisions 
given  will  be  added  to  the  degrees  and  minutes  originally  ob- 
tained on  the  arc,  and  the  sum  of  the  two  will  be  the  altitude. 
To  this  altitude  will  be  applied  the  index  error  (if  any  exists)  in 
order  to  obtain  the  corrected  observed  angle. 

Remarks. — The  quadrant,  octant,  and  sextant  are  constructed 
on  the  same  principle.  Although  the  real  arcs  of  these  instru- 


132  THE  NAVIGATOR'S  POCKET-BOOK 

merits  are  respectively  only  45°,  60°,  and  70°,  yet  owing  to  their 
double  reflection  they  measure  angles  of  90°,  120°,  and  140°. 

SHADE-GLASSES.— (See  Sextant.) 

SHADOW-PIN. — A  straight,  slender  pin  arranged  to  stand 
vertically  on  the  centre  of  the  glass  of  the  compass  bowl.  It  is 
portable  and  is  set  in  place  when  required  for  the  purpose  of 
obtaining  bearings  of  the  sun.  As  its  name  indicates,  it  casts  a 
shadow,  and  the  opposite  point  of  the  compass  from  that  on 
which  the  shadow  falls  is  accepted  as  the  bearing  of  the  body. 
The  shadow-pin  may  be  employed  for  taking  bearings  generally, 
but  it  is  not  as  satisfactory  as  an  azimuth  attachment  or  the 
pelorus. 

SHAPING  THE  COURSE.— (See  Chart  Sailing  ;  Great- 
Circle  Sailing  ;  Mercator's  Sailing  ;  Middle-Latitude  Sailing.) 

SHIP  TIME. — The  hour  shown  by  the  ship's  clock,  which 
is  set  to  apparent  time  or  solar  time.  This  may  be  done  roughly 
by  turning  the  hands  of  the  clock  to  twelve  (noon)  when  the  sun 
crosses  the  meridian,  or  by  allowing  for  the  number  of  miles 
sailed  ^east  or  west  since  the  clock  was  last  set.  To  accomplish 
this  simply  add  to  the  face  of  the  clock  four  minutes  of  time  for 
every  degree  sailed  east  and  subtract  four  minutes  for  every  de- 
gree sailed  west  since  the  clock  was  last  set  on  solar  time.  The 
most  correct  way  is  to  proceed  according  to  the  rule  given  under 
the  head  of  Regulating* 

SHORE  RATE.— (See  Rate.) 
SIDEREAL — Relating  to  the  stars. 

SIDEREAL  DAY. — The  interval  between  two  successive 
transits  of  the  same  star  over  the  same  meridian  ;  the  period  of 
time  in  which  the  earth  performs  a  complete  revolution  on  its 


THE  NAVIGATOR'S  POCKET-BOOK  133 

axis.  The  length  of  a  sidereal  day  is  23  h.  56  m.  04  sec.,  so  that 
a  sidereal  day  is  shorter  than  a  mean  solar  day  by  3  m.  56  sec. 

SIDEREAL  NOON.— This  occurs  when  the  First  Point  of 
Aries  comes  to  the  meridian. 

SIDEREAL  TIME.— Time  measured  by  the  stars.  Sidereal 
time  commences  when  the  First  Point  of  Aries  is  on  the  me- 
ridian and  is  counted  from  one  hour  to  twenty-four  hours,  when 
the  same  point  returns  to  the  meridian  again. 

SIGHT.— To  take  a  sight  is  to  measure  the  altitude  of  a 
heavenly  body. 

SLIDING  LIMB.— (See  Sextant.) 

SLIP  OF  WHEEL — The  difference  between  the  speed 
shown  by  a  steam  vessel  and  the  speed  that  would  be  attained 
provided  the  propeller  or  paddle-wheels  acted  upon  a  solid  sub- 
stance in  place  of  a  fluid.  Slip  of  wheel  is  often  referred  to  as 
the  lost  motion  of  the  propeller.  It  is  customary  to  allow  a  cer- 
tain number  of  revolutions  to  the  mile,  and  according  to  this  the 
estimated  distance  run  by  the  vessel  is  compared  with  the  actual 
distance  run  by  observation,  and  the  difference,  expressed  as  a 
per  centum,  is  entered  in  the  log-book  under  the  head  of  slip  of 
wheel.  Head  winds  and  seas  often  retard  a  vessel's  speed  so  that 
the  slip  of  wheel  reaches  50  per  cent,  and  more. 

SOLAR. — Relating  to  the  sun. 

SOLAR  DAY. — The  time  which  elapses  between  two  succes- 
sive transits  of  the  sun  over  the  same  meridian. 

SOLAR  SYSTEM.— The  sun  and  the  heavenly  bodies  revolv- 
ing around  it ;  namely  :  Mercury,  Venus,  Earth,  Moon,  Mars, 
Jupiter,  Saturn,  Uranus,  and  Neptune. 

SOLAR  TIME. — Time  measured  by  the  sun.    When  the  sun 


134  THE  NAVIGATOR'S  POCKET-BOOK 

crosses  the  meridian  of  the  observer  it  is  apparent  noon  at  hk 
place. 

SOLSTICES. — Those  times  of  the  year  when  the  sun  is  at  its 
greatest  distance  from  the  equator  ;  when  its  declination  is  23|° 
north  or  23^°  south. 

SPECULUM. — A  mirror  ;  the  reflecting  glass  on  an  azimuth 
attachment. 

SPHERE.— According  to  geography,  a  representation  of  the 
earth's  surface,  and  according  to  astronomy,  the  celestial  con- 
cave. 

SPHERICAL.— Globular. 

SPHERICAL  SAILINGS.— Great-Circle,  Mercator,  Middle- 
Latitude  and  Parallel  Sailings. 

SPHERICAL  TRIANGLE.— A  portion  of  the  surface  of  a 
sphere,  contained  by  the  arcs  of  three  great  circles. 

SPHERICAL  TRIGONOMETRY.— That  branch  of  trig- 
onometry which  deals  with  the  method  of  solving  spherical 
triangles. 

SPIRIT  COMPASS. — A  liquid  compass. 

SPRING  EQUINOX. — When  the  sun  crosses  the  equator 
from  southern  into  northern  declinations.  This  is  known  as  the 
First  Point  of  Aries.  The  Spring  Equinox  is  often  referred  to  as 
the  Vernal  Equinox.  (See  First  Point  of  Aries.) 

STANDARD  COMPASS. — One  of  the  ship's  compasses 
placed  where  it  is  least  influenced  by  deviation,  and  by  which 
the  vessel  is  navigated. 

STANDARD  TIME.— Time  shown  by  a  watch  or  clock  set 
to  mean  solar  time.  (See  Mean  Sun.) 


THE  NAVIGATOR'S  POCKET-BOOK  135 

STARS.— (See  Fixed  Stars.) 

STAR  TELESCOPE.— (See  Sextant.) 

STAR  TIME. — Same  as  sidereal  time. 

STATION  POINTER.— An  instrument  made  use  of  in  ma- 
rine surveying.  It  consists  of  a  circle  of  brass  graduated  in  de- 
grees, and  is  provided  with  one  fixed  and  two  movable  arms 
which  project  from  its  centre,  so  that  the  former  may  be  set  to 
any  required  angle.  It  is  used  sometimes  on  board  ship  when 
sailing  along  the  coast,  so  as  to  locate  the  vessel's  position  by 
observing  bearings  of  objects  on  shore.  (See  Telemeter.) 

STATUTE  MILE.— (See  Mile.) 

STEERING  COMPASS — That  particular  compass  referred 
to  by  the  wheelsman  in  steering  the  ship.  The  vessel  is  placed 
on  her  course  by  the  standard  compass,  then  whatever  point  is 
indicated  at  the  time  by  the  steering  compass  shows  the  course 
for  the  wheelsman  to  keep  the  vessel  on  according  to  that  com- 
pass. 

STELLAR — Relating  to  the  stars. 

SUB-PERMANENT  MAGNETISM.— After  a  new  iron 
ship  has  been  launched,  it  has  been  found  that  the  magnetism 
induced  in  the  hull  while  building  rapidly  diminishes,  but  by 
no  means  departs  entirely,  and  that  which  remains  is  called  sub- 
permanent  magnetism. 

SUMNER'S  METHOD. — A  process  employed  for  finding 
by  a  chronometer  observation  of  the  sun,  or  other  heavenly 
body,  the  true  latitude  and  longitude  of  the  ship,  especially  when 
the  latitude  by  dead  reckoning  cannot  be  relied  upon.  This  is 
one  of  the  most  valuable  problems  within  the  sphere  of  the 
navigator,  and  should  be  practised  by  him  until  proficiency  is 


136  THE   NAVIGATORS   POCKET-BOOK 

attained.  In  reality  it  consists  of  simply  working  out  the  lon- 
gitude several  times  by  either  the  sun  or  the  moon,  a  planet  or 
fixed  star.  In  the  following  we  will  consider  that  the  sun  is 
employed,  consequently  the  longitudes  will  be  ascertained 
according  to  the  rule  given  under  the  head  of  "Longitude  by 
One  Altitude  of  the  Sun."  In  case  this  problem  is  worked  by 
the  moon  or  by  a  planet  or  a  star,  then  the  longitudes  will  be 
found  according  to  the  respective  rules  given  for  those  bodies 
under  the  head  of  Longitude  ;  but  the  lines  on  the  chart  will  be 
drawn  and  the  position  of  the  vessel  plotted  in  precisely  the 
same  way  as  described  below  for  the  sun.  This  problem  in 
character  is  similar  to  and  its  result  the  same  as  that  derived 
from  what  is  known  as  the  Combined  Altitude  Problem,  or  the 
Double  Altitude  Problem,  but  it  employs  fewer  figures  and  as  a 
natural  consequence  is  simple  in  comparison  and  more  easily 
worked  than  the  other. 

Rule. — Assume  two  latitudes,  one  30'  (miles)  less,  and  the 
other  30'  greater  than  the  latitude  by  dead  reckoning,  then  ob- 
serve a  regular  time  sight  of  the  sun  and  work  it  up  as  usual, 
employing  either  of  the  assumed  latitudes,  and  mark  the  result 
on  the  chart.  Now  work  the  same  sight  over  again,  using  the 
other  assumed  latitude.  Mark  this  answer  also  on  the  chart  and 
draw  a  pencil  line  from  one  dot  to  the  other.  This  is  known  as 
a  line  of  bearing,  and  the  ship  will  be  somewhere  on  this  line. 

The  next  thing  required  is  to  locate  the  vessel  on  this  line  of 
bearing.  To  effect  this  wait  until  the  sun  has  changed  its 
azimuth  (bearing)  at  least  2-$-  points  (four  or  more  would  be 
better)  then  observe  another  regular  time  sight  and  work  it  up 
twice  as  before,  making  use  of  the  same  two  assumed  latitudes. 
Mark  these  two  results  on  the  chart  and  connect  them  also  with 
a  pencil  line,  which  call  the  second  line  of  bearing.  It  will  be 


THE  NAVIGATOR'S  POCKET-BOOK  137 

seen  that  the  first  and  second  pencil  lines  cross  one  another. 
Now  this  intersection  points  out  the  ship's  place  provided  she 
has  remained  stationary  between  observations,  but  if  not,  then 
the  course  and  distance  sailed  after  the  first  observation  was 
taken  must  be  considered  as  follows  : 

Lay  off  (in  pencil)  from  any  part  of  the  first  line  of  bearing 
the  true  course  and  distance  sailed  in  the  interval  between 
sights,  and  through  the  termination  of  this  course  and  distance 
draw  a  line  parallel  to  the  first  line  of  bearing,  and  where  this 
last  line  drawn  intersects  the  second  line  of  bearing  will  be  the 
ship's  place. 

Remarks.—  Instead  of  using  assumed  latitudes  30'  different 
from  the  latitude  by  account,  the  navigator  may  extend  this 
amount  to  1°  if  he  so  prefers. 

When  the  first  line  is  drawn  on  the  chart  for  the  purpose  of 
connecting  the  first  two  pencil  dots,  the  navigator  knows  that 
he  is  somewhere  on  this  line,  and  provided  the  line  is  not  paral- 
lel to  the  coast,  its  extension  will  run  into  the  land,  so  that  if 
the  ship  is  headed  to  sail  on  this  line  of  bearing  toward  the 
coast,  she  will  ultimately  reach  the  point  into  which  the  line 
runs.  The  same  applies  as  well  to  the  second  line  of  bearing. 

It  has  already  been  explained  that  when  the  second  line  of 
bearing  has  been  drawn  on  the  chart,  the  ship's  place  is  fixed. 

This  problem  has  been  styled  by  some  navigators  as  an  astro- 
nomical cross-bearing. 

SUN.— The  centre  of  the  solar  system  :  diameter,  885,000 
miles  ;  mean  distance  from  the  earth,  95,000,000  miles  ;  mean 
apparent  diameter,  32'  ;  circumference,  2,780,000  miles. 

SUN  DOG. — A  luminous  spot  occasionally  seen  in  the  heavens 
near  the  sun. 


138  THE   NAVIGATOR^  POCKET-BOOK 

SUNRISE  AND  SUNSET  SIGHTS.— (See  Longitude.) 
SUN  TIME. — Same  as  solar  time. 

SWINGING  SHIP — When  the  vessel  is  turned  in  a  circle 
so  that  her  head  is  brought  consecutively  to  the  thirty-two 
points  of  the  compass,  the  operation  is  known  as  swinging  ship. 
This  is  performed  in  compass-adjusting,  the  purpose  being  to 
note,  while  on  each  point,  the  compass-bearing  of  some  distant 
but  well-defined  object,  the  correct  magnetic  bearing  of  which 
is  known. 

SYMBOLS.— (See  Log  Book.) 

TAFFRAIL  LOG. — A  patent  log,  the  register  of  which  se- 
cures to  the  taffrail.  (See  Patent  Log.) 

TAKING  DEPARTURE.— (See  Departure.) 

TANGENT  SCREW.— (See  Sextant.) 

TELEMETER — An  instrument  consisting  of  two  parallel 
base  bars,  divided  by  scales  to  tenths  of  an  inch  and  ranging  from 
0  to  20  inches  on  each  bar.  The  object  of  this  instrument  is  to 
mechanically  solve  problems  that  involve  the  parts  of  a  plane 
triangle.  It  is  only  of  use  when  sailing  along  the  coast,  when 
it  affords  a  ready  means  of  locating  the  ship  by  observing  shore 
bearings,  such  as  light-houses,  prominent  headlands,  etc. 

TELL-TALE. — An  inverted  compass  suspended  from  over- 
head in  the  cabin,  or  elsewhere  below. 

TERRESTRIAL.— Relating  to  the  earth. 

TERTIARY- MERIDIANS. — Those  connected  with  second- 
ary meridians  by  carrying  time  in  the  most  careful  manner.  (See 
Secondary  Meridians.) 

THERMOMETER. — An  instrument  used  for    measuring 


THE  NAVIGATOR'S  POCKET-BOOK  139 

the  variations  of  temperature.  Fahrenheit's  thermometer  is  a 
mercurial  column  so  graduated  as  to  have  180°  between  the 
freezing  and  boiling  points  of  water.  The  freezing  point  of 
water  on  this  thermometer  is  32°,  and  the  boiling  point  212°. 
To  indicate  degrees  below  zero,  it  is  common  to  preface  them 
with  the  minus  ( — )  sign.  A  Centigrade  thermometer  is  a  mer- 
curial column  so  graduated  as  to  have  100°  between  the  freezing 
and  boiling  points  of  water,  zero  being  the  freezing  point. 

To  reduce  Centigrade  reading  to  Fahrenheit,  multiply  by  9, 
divide  by  5  and  add  32. 

To  reduce  Fahrenheit  to  Centigrade,  subtract  32,  multiply  by 
5  and  divide  by  9. 

TIME. — (See  Apparent,  Astronomical,  Civil,  Greenwich, 
Local- Apparent,  Mean,  Mean-Solar,  Ship,  Sidereal,  Solar,  Stand- 
ard, Star,  and  Sun  Times.  See  also  Equation  of  Time.) 

TIME  COURSE. — During  fog,  while  navigating  in  waters 
where  it  is  necessary  to  change  the  course  at  certain  fixed  points 
in  order  to  keep  in  the  channel,  or  to  avoid  danger,  the  employ- 
ment of  time  courses  becomes  imperative.  In  order  to  run  these, 
the  course  and  distance  from  point  to  point  is  measured  on  the 
chart,  and  the  speed  of  the  vessel  taken  into  account.  As  soon 
as  the  calculated  period  of  time  has  expired,  it  is  considered  that 
the  required  distance  has  been  run,  and  the  course  is  accord- 
ingly changed. 

If  there  is  a  current  flowing  with,  or  against,  or  across  the 
ship's  course,  the  same  must  be  allowed  for. 

When  threading  coral  reefs  that  are  submerged,  time  courses 
are  often  employed. 

TIME  SIGHT.— An  observation  of  a  heavenly  body  taken 
for  the  purpose  of  ascertaining  the  longitude.  (See  Longitude.) 


140  THE  NAVIGATOR'S  POCKET-BOOK 

TRANSIT. — The  passage  of  a  heavenly  body  across  the 
meridian.  (See  Lower  Transit ;  Upper  Transit.) 

TRAVERSE. — An  irregular  track  made  by  a  vessel  on  ac- 
count of  having  sailed  several  courses. 

TRAVERSE  SAILING.— (See  Traverse.) 

TRAVERSE  TABLES.— Tables  containing  the  difference 
of  latitude  and  departure  for  quarter  points  and  for  single  de- 
grees of  the  compass,  calculated  for  intervals  of  one  mile  and 
extending  to  three  hundred  miles.  By  these  tables  the  solution 
of  right-angle  triangles  is  accomplished  by  mere  inspection.  The 
form  that  a  navigator  rules  for  working  out  his  dead  reckoning 
is  a  traverse  table  for  the  particular  courses  sailed  by  his  ves- 
sel. 

TRIGONOMETRY. — The  science  of  measuring  triangles. 

TRIPOD  COMPASS. — A  compass  elevated  on  a  three-leg 
stand,  on  the  principle  of  the  pole  compass. 

TROPIC  OF  CANCER.— The  parallel  of  23°  28'  north— 
the  highest  northern  point  of  the  sun's  declination,  which  it 
reaches  on  June  21st. 

TROPIC  OP  CAPRICORN.— The  parallel  of  23°  28'  south 
— the  highest  southern  point  of  the  sun's  declination,  which  it 
reaches  on  December  21st. 

TRUE-CENTRAL-ALTITUDE.  — (See  Corrected  Alti- 
tude.) 

TYPHOON.— (See  Law  of  Storms.) 

UPPER  LIMB. — The  highest  part  of  the  circumference  of 
the  sun  and  moon  ;  the  part  situated  directly  above  the  centre. 
When  the  image  of  the  lower  portion  of  the  disk  of  the  sun  or 
moon  is  brought  in  contact  with  the  horizon,  it  is  said  that  the 


THE  NAVIGATOR'S  POCKET-BOOK  141 

altitude  of  the  lower  limb  is  observed,  and  when  the  image  of 
the  upper  portion  of  the  disk  is  brought  iii  contact  with  the  hori- 
zon, it  is  said  that  the  altitude  of  the  upper  limb  is  observed. 
(See  Corrected  Altitude.) 

UPPER  TRANSIT. — The  passage  of  a  heavenly  body  over 
the  meridian  when  the  body  is  moving  from  east  to  west.  The 
Nautical  Almanac  gives  the  astronomical  times  of  the  upper 
transits  of  heavenly  bodies.  The  body  having  risen  until  it 
crossed  the  meridian  above  the  pole,  while  moving  from  east  to 
west,  it  declines  to  the  west,  then  curves  eastward,  continuing 
to  fall  until  it  crosses  the  meridian  below  the  pole — 180°  distant 
from  the  meridian  of  its  upper  transit.  It  then  commences  to 
rise,  still  moving  eastward,  and  when  midway  between  the 
meridians  of  its  upper  and  lower  transits,  it  curves  westward 
and  continues  to  rise  until  it  again  makes  its  upper  transit.  (See 
Lower  Transit.) 

VARIATION. — The  divergence  of  the  compass  needle  from 
the  true  north  of  the  heavens.  This  is  not  constant.  In  the 
year  1663  in  Paris,  the  needle  pointed  true  north,  previous  to 
which  the  variation  had  been  easterly.  From  the  year  1663  to 
the  year  1814,  the  westerly  variation  in  Paris  steadily  increased, 
until  in  the  latter  year  it  amounted  to  22£°.  From  the  year  1814 
it  has  steadily  decreased,  but  is  still  westerly.  (See  Compass  ; 
Amplitude  ;  Azimuth.) 

VARIATION  CHART.— (See  Chart.) 
VERNAL  EQUINOX.— <See  Spring  Equinox.) 

VERNIER. — The  graduated  scale  on  the  sliding  limb  or  in. 
dex  bar  of  the  sextant.  (See  Sextant.) 

VERTEX. — That  point  of  the  heavens  situated  perpendicu 


142  THE  NAVIGATOR'S  .POCKET-BOOK 

Jarly  above  the  observer's  head  ;  the  angular  point,  or  the  point 
where  the  two  legs  or  sides  of  an  angle  meet. 

VERTICAL. — Perpendicular  to  the  horizon. 

VERTICAL  CIRCLE. — A  great  circle  of  the  sphere  which 
passes  through  the  zenith  and  nadir  of  a  place. 

VERTICAL  DANGER  ANGLE.— (See  Danger  Angle.) 

VISIBLE  HORIZON. — The  boundary  or  limit  of  the  obser- 
ver's view  is  termed  the  visible  or  apparent  horizon.  The  angle 
between  the  sensible  and  visible  horizons  is  known  as  the  dip  of 
the  horizon. 

WATCHES.— (See  Log-Book.) 

WEATHER. — The  signs  or  indications  by  which  the  coming 
weather  may  be  anticipated  are  as  follows  : 

A  rosy  sky  at  sunset,  tine  weather  ;  a  bright  yellow  sky  at 
sunset,  wind  ;  a  pale  yellow  sky  at  sunset,  wet ;  orange  or  cop- 
per colored  sky,  wind  and  rain  ;  sickly  greenish  hue,  wind  and 
rain  ;  tawny  or  coppery  clouds,  wind  ;  a  dark  red  sky,  rain  ; 
a  red  sky  in  the  morning,  bad  weather  ;  a  gray  sky  in  the  morn- 
ing, fine  weather  ;  a  high  dawn,  wind  ;  a  low  dawn,  fair 
weather  ;  soft  or  delicate  clouds,  fine  weather  with  light  breezes  ; 
hard-edged,  oily  looking  clouds,  wind  ;  a  dark,  gloomy,  blue 
sky,  wind  ;  light,  bright-blue  sky,  fine  weather  ;  light,  delicate 
tints  with  soft,  indefinite  forms  of  cloud,  fine  weather  ;  gaudy 
or  unusual  hues  with  hard,  definitely  outlined  clouds,  rain  and 
wind  ;  small,  inky  clouds,  rain  ;  high  upper  clouds  crossing  the 
heavens  in  a  direction  different  from  that  of  the  lower  clouds,  or 
of  the  wind  felt  below,  foretell  a  change  of  wind  in  the  direc- 
tion of  the  upper  clouds  ;  when  sea  birds  fly  out  far  to  seaward, 
moderate  wind  and  fair  weather  may  be  expected ;  when  sea 


THE  NAVIGATOR'S  POCKET-BOOK  143 

birds  bang  about  the  land  or  fly  inland,  strong  winds  and  stormy 
weatber  are  promised  ;  dew  is  an  indication  of  coming  fine 
weather. 

Cirrus. — Also  known  as  the  mare-tail  cloud,  composed  of 
streaks,  wisps,  and  fibres  ;  a  cloud  of  the  least  density  and 
greatest  elevation,  showing  the  widest  range  of  direction  and 
variety  of  form.  Settled  weather  is  to  be  expected  when  groups 
of  cirri  are  to  be  seen  during  a  gentle  wind  after  severe  weather 
has  been  experienced.  When  streaks  of  cirri  extend  across  the 
sky  conforming  to  the  direction  in  which  a  light  wind  is  blow- 
ing, the  wind  will  remain  steady  but  increase.  When  fine 
threads  of  cirri  are  blown  or  brushed  backward  at  one  end,  the 
surface  wind  will  veer  around  to  that  point. 

Cumulus.— This  is  also  known  as  the  day  cloud  and  the  sum- 
mer  cloud.  It  forms  only  in  the  day-time  during  the  summer, 
and  results  from  the  rise  of  vapors  from  rivers,  lakes,  etc.,  into 
the  colder  atmosphere.  Fine,  calm,  and  warm  weather  may  be 
anticipated  when  cumuli  take  on  a  moderate  size  and  delicate 
color ;  but  cold,  rainy,  and  heavy  weather  may  be  expected 
when  cumuli  in  dense,  dark  masses  roll  acress  the  sky,  sink  low- 
er, and  do  not  disappear  at  sunset. 

Stratus — Also  called  the  night  cloud.  It  hangs  the  lowest  of 
the  various  clouds,  obtains  its  greatest  density  about  midnight, 
and  disappears  when  the  sun  rises.  It  is  formed  by  the  conden- 
sation of  vapors  from  lakes,  marshes,  etc.,  appearing  as  an  ex 
tended  sheet  of  white  mist  near  to  the  earth,  and  sometimes 
touching  it. 

Cirro-Cumulus. — This  is  known  as  well  by  the  name  of  a 
mackerel  sky.  It  is  seen  in  small,  rounded  masses,  looking  like 
flocks  of  sheep  lying  down,  and  in  consequence  is  referred  to  at 
times  as  sheep  in-a -meadow  sky.  It  is  principally  seen  in  summer, 


144  THE  NAVIGATOK'S  POCKET-BOOK 

and  indicates  warm,  dry,  weather.  When  cirro-cumulus  occurs 
in  winter,  a  thaw  and  wet  weather  may  be  expected. 

Cirro-Stratus. — Also  referred  to  as  the  vane  cloud,  the  shoal 
of-fisli  cloud,  and  the  mackerel-backed  cloud.  A  storm  of  rain  or 
snow  may  be  expected  when  this  cloud  is  seen.  As  it  name  sig- 
nifies, this  cloud  exhibits  a  mingling  of  the  characteristics  of 
the  cirrus  and  stratus,  being  dense  in  the  middle  and  tapering 
toward  the  edges. 

Cumulo-Stratus. — A  blending  or  mingling  of  the  cumulus 
and  cirro-stratus,  appearing  at  times  as  a  thick  bank  of  cloud 
with  overhanging  edges.  What  is  known  as  a  distinct-cumulo- 
stralus  cloud  appears  as  a  cumulus  cloud  surrounded  on  all  sides 
by  small  fleecy  clouds.  When  cumulo-stratus  clouds  are  seen 
sudden  atmospheric  changes  may  be  expected. 

Nimbus,  or  Cumulo-Cirro-  Stratus. — Called  the  rain  cloud. 
As  it  name  signifies,  it  is  a  combination  of  the  three  primary 
forms  of  cloud.  The  cirro-stratus  overspreads  the  sky,  and  un- 
derneath it  the  cumulus  clouds  drive  in  from  windward  until 
they  form  one  continuous  mass,  settling  down  in  a  horizontal 
sheet  from  which  rain  falls. 

Cloud  Scale. — The  amount  of  cloud  is  denoted  by  a  numer- 
ical scale  of  0  to  10—0  indicating  a  clear  sky,  5  a  sky  half  cov- 
ered, and  10  a  totally  obscured  sky. 

Rainbows. — When  rainbows  are  observed  in  the  morning 
they  promise  wet  weather,  but  when  observed  in  the  ^veiling 
they  promise  clear  weather. 

WIND. — The  wind,  as  a  rule,  shifts  with  the  sun ;  but 
whereas  this  means  from  left  to  right  (or  with  the  hands  of  a 
clock)  in  the  northern  hemisphere,  it  means  from  right  to  left 
(or  against  the  hands  of  a  clock)  in  the  southern  hemisphere. 
This  is  known  as  veering.  When  the  wind  shifts  in  the  contrary 


THE  NAVIGATOR'S  POCKET-BOOK  145 

direction  it  is  known  as  backing.    There  is  an  old  sea  couplet 
which  applies  with  truthfulness  to  the  shifting  of  the  wind  •. 

"  When  the  wind  shifts  against  the  sun, 
Trust  it  not,  for  back  it  will  run." 

In  the  northern  hemisphere  the  veering,  or  proper  shifting  of 
the  wind  would  be  from  east  to  west  by  the  way  of  south-east, 
south,  and  south-west,  and  the  backing  of  the  wind  would  be 
from  east  to  west  by  the  way  of  north-east,  north,  and  north- 
west. 

In  the  southern  hemisphere  the  above  rule  would  be  reversed. 

When  the  wind  backs  it  may  be  accepted  as  a  sign  that  the 
weather  is  unsettled,  and  that  the  wind  will  come  out  again  from 
its  original  quarter. 

Winds  are  named  from  the  direction  in  which  they  blow, 
hence  a  north  wind  comes  out  of  the  north. 

ZENITH. — That  point  in  the  heavens  vertically  overhead  of 
the  observer,  and  90°  distant  from  every  point  of  the  horizon. 
Opposed  to  nadir.  (See  Nadir.) 

ZENITH  DISTANCE.— What  an  altitude  lacks  of  90°,  or 
the  complement  of  an  altitude  ;  the  angular  distance  of  a  heav- 
enly body  from  the  zenith  of  the  observer. 

ZERO. — The  point  at  which  the  cutting  or  graduation  of  a 
sextant,  etc.,  commences. 

ZODIAC. — An  imaginary  zone  in  the  celestial  concave  in 
which  the  sun,  moon,  and  larger  planets  appear  to  perform  their 
revolutions. 

ZONE.— There  are  five  zones  :  the  torrid  zone  extending 
10 


146  THE  NAVIGATOR'S  POCKET-BOOK 

from  the  equator  to  23°  28'  north  and  south  ;  the  temperate  zones 
extending  from  23°  28'  north  and  south  to  66°  32'  north  and  south, 
and  the  frigid  zones  extending  from  66°  32'  north  and  south  to  the 
poles. 

ADDENDA. 

ARC  INTO  TIME  AND  VICE  VERSA. — To  reduce  longi- 
tude (arc)  into  time,  and  time  into  longitude,  the  use  of  Table  7, 
Bowditch,  is  recommended.  In  the  first  column  of  said  table  the 
degrees  of  longitude  are  found  at  the  top  marked  D,  and  the 
minutes  of  longitude  underneath  marked  M.  In  the  adjoining 
column  to  the  right  is  found  the  corresiponding  time — hours 
marked  H  on  top  and  minutes  of  time  marked  M  underneath. 
The  explanation  of  this  is  that  when  the  arc  column  is  used  for 
degrees,  the  answer  opposite  in  the  time  column  is  given  in  hours 
and  minutes ;  but  when  the  arc  column  is  used  for  minutes  of 
longitude  the  answer  opposite  in  the  time  column  is  given  in 
minutes  and  seconds. 

If  the  arc  column  is  used  for  seconds  of  longitude,  the  answer 
opposite  in  the  time  column  is  given  for  seconds  and  sixtieths  of 
seconds. 

To  convert  time  into  longitude  (arc)  apply  the  hours  under  H 
in  the  time  column,  and  opposite  to  the  left  in  the  arc  column  will 
stand  the  value  in  degrees.  Next  put  the  minutes  of  time  under 
M  in  the  time  column  and  opposite  to  the  left  in  the  arc  column 
will  stand  the  value  in  minutes  of  arc. 

If  one  second  of  time  is  left  over,  its  value  in  arc  is  15";  if  two 
seconds  of  time  are  left  over,  their  value  in  arc  is  30",  and  if  three 
seconds  of  time  are  left  over,  their  value  in  arc  is  45".  (See  Cor- 
recting Time;  Chronometer;  Ship's  Time;  Regulating;  Time.) 

BACKING  AND  FILLING  PROBLEM.— After  taking  a 
morning  sight  for  longitude,  the  figures  are  held  for  the  time 
being,  as  it  is  not  considered  possible  to  work  the  problem  at  once 
with  any  reliance  upon  the  result  owing  to  the  latitude  by  dead 
reckoning  being  in  doubt.  Therefore,  the  course  and  distance 
sailed  by  the  ship  in  the  interval  between  the  morning  sight  and 
noon  are  carefully  noted  so  that  the  navigator  may  work  back  by 
dead  reckoning  from  his  noon  latitude  by  observation  to  the  lat'i- 


THE  NAVIGATOR'S  POCKET-BOOK  147 

tude  his  ship  was  in  at  the  time  of  the  morning  altitude.  Having 
done  this,  his  morning  longitude  may  be  worked  out,  and  then 
brought  forward  to  noon  by  dead  reckoning.  It  is  this  going 
backward  and  bringing  forward  that  gives  the  name  to  this  style 
of  problem.  The  first  thing  to  do  is  to  work  out  the  noon  lati- 
tude, then  the  latitude  of  the  ship  at  the  time  of  the  morning 
sight,  then  the  longitude  at  the  time  of  the  morning  sight,  and 
then  bring  the  latter  forward  to  noon. 

CHART  SAILING.— On  page  25,  under  the  head  of  Cross 
Bearings  it  refers  to  the  conversion  of  compass  bearings  (where 
deviation  exists)  into  correct  magnetic  bearings.  This  is  done  by 
applying  to  the  two  bearings  respectively  the  amount  of  deviation 
existing  for  the  ship's  head  at  the  time  the  bearings  were  taken. 
To  effect  this  simply  allow  westerly  deviation  around  the  compass 
contrary  to  the  way  the  hands  of  a  watch  revolve,  and  easterly  de- 
viation with  the  hands  of  a  watch.  By  applying  the  given  amount 
of  deviation  in  this  way  the  compass  bearings  will  be  converted 
into  correct  magnetic  bearings,  and  these  will  be  plotted  on  the 
chart. 

For  example,  suppose  a  light-house  bears  N.  by  compass  and 
there  is  one  point  of  westerly  deviation  to  allow  for ;  in  this  case 
the  correct  magnetic  bearing  will  be  N.  by  W.,  which,  in  other 
words,  is  the  way  the  light-house  would  bear  by  the  ship's  com- 
pass if  there  was  no  deviation. 

On  the  other  hand,  if  there  was  one  point  of  easterly  deviation 
to  allow  for,  then  the  correct  magnetic  bearing  of  the  light-house 
would  be  N.  by  E. 

CHRONOMETER  TO  SHIP'S  TIME.— To  find  the  mean 
time  at  the  ship  from  the  chronometer  or  Greenwich  time,  pro- 
ceed as  follows : 

By  the  use  of  Table  7  turn  the  ship's  longitude  into  time,  then 
add  same  to  the  face  of  the  chronometer  if  in  east  longitude,  but 
subtract  it  if  in  west  longitude,  and  the  answer  will  be  the  local 
mean  time  at  the  ship. 

If  the  local  apparent  time  at  the  ship  is  required,  simply  apply 
the  equation  of  time  for  the  given  day  according  to  the  directions 
given  in  the  Nautical  Almanac.  (See  Regulating,  Time.) 

CORRECTING  TIME.— When  the  ship  changes  her  longi- 
••iide  she  changes  her  time,  and  the  method  of  estimating  this 
change  is  as  follows  : 


148  THE  NAVIGATOR'S  POCKET-BOOK 

Note  the  compass  course  and  distance  sailed  since  the  clock 
was  last  set,  and  convert  said  course  into  a  true  course  by  apply- 
ing leeway,  variation  and  deviation  ;  then  from  the  table  select 
the  departure  made  for  said  course  and  distance  and  turn  this  de- 
parture into  longitude  according  to  the  parallel  of  the  ship.  Next 
multiply  this  change  of  longitude  by  4,  which  will  reduce  it  to 
seconds  of  time,  then  apply  this  change  of  time  to  the  face  of  the 
clock,  adding  if  the  ship  has  sailed  east,  but  subtracting  if  she 
has  sailed  west,  and  the  answer  will  be  the  time  of  the  meridian 
the  ship  is  on.  Sailing  north  or  south  does  not  change  time. 
(See  Regulating,  Time.) 

DEAD  RECKONING. — In  seeking  in  Tables  1  or  2  for  the 
distance  run  on  a  certain  course,  if  the  number  of  miles  exceed 
the  figures  in  the  distance  column  (which  extend  to  300  miles 
only)  then  take  out  the  latitude  and  departure  for  half  the  distance 
run,  and  multiply  the  same  by  2. 

On  the  same  principle,  when  seeking  to  find  the  course  and  dis- 
tance made  good,  if  the  difference  of  latitude  and  departure  are 
too  great  for  comparison,  point  off  a  place  in  each,  which  will  re- 
duce the  quantities  to  one- tenth  of  their  values,  then  make  the 
comparison  as  usual,  and  multiply  the  number  of  miles  given  by 
10  ;  but  do  not  multiply  the  course  angle,  for  the  same  has  been 
preserved  by  reducing  the  difference  of  latitude  and  departure 
proportionately. 

LATITUDE  BY  THE  POLE  STAR — The  way  to  find  the 
latitude  of  the  ship  by  the  Pole  Star,  using  what  is  commonly 
called  the  "clock  method,"  is  fully  treated  in  this  book  on  page 
76.  The  '*  chronometer  method  "  is  as  follows: 

Observe  an  altitude  at  any  hour  when  the  star  can  be  seen,  note 
the  chronometer  and  convert  same  into  astronomical  time.  To 
this  latter  apply  the  ship's  longitude  in  time,  adding  it  if  in  east 
longitude  but  subtracting  it  if  in  west,  and  the  answer  will  be  the 
astronomical  mean  time  at  ship.  To  this  add  the  correction 
from  Table  3,  nautical  almanac,  then  to  this  sum  add  the  right 
ascension  of  the  mean  sun  for  the  given  day,  which  will  show 
the  local  sidereal  time.  This  applied  to  the  almanac  constant 
will  i»;ive  the  hour  angle.  Next  correct  the  altitude  for  dip 
and  refraction,  then  apply  to  the  remainder  the  correction  given 
for  the  star's  hour  angle,  and  the  answer  will  be  the  latitude  of 
the  ship. 


THE   NAVIGATOR'S    POCKET-BOOK 


149 


LEAD  AND  LINE.— The  hand-lead  is  about  10  inches  in 
length,  tapering  to  its  upper  end  where  the  line  is  bent  in,  and 
weighs  about  10  pounds.  The  line  measures  25  fathoms  (150  feet), 
and  this  instrument  is  employed  for  taking  soundings  in  water  of 
20  fathoms  and  under — the  other  5  fathoms  being  surplus  line. 
The  lead  has  9  marks  and  11  deeps— the  latter  being  the  unmarked 
fathoms  of  the  line.  The  following  shows  the  manner  of  marking; 
At  2  fathoms  from  the  lead,  2  strips  of  leather. 


3  strips  of  leather, 
piece  of  white  bunting, 
piece  of  red  bunting, 
leather  with  a  hole  in  it. 
piece  of  blue  bunting, 
piece  of  white  bunting, 
piece  of  red  bunting, 
strand  with  two  knots. 


At  3 
At  5 

At  7 
At  10 
At  13 
At  15 

At  17 
At  20 

LONG  DAY. — Should  a  vessel  sail  from  port  early  in  the 
morning  and  get  clear  of  land  and  be  on  her  course  before  noon, 
it  is  customary  with  the  navigators  to  make  no  attempt  to  work 
out  the  position  of  the  ship  until  the  following  noon.  This  in- 
sures more  than  a  24  hours'  reckoning,  and  is  referred  to  as  a 
long  day's  work.  On  the  other  hand,  if  the  vessel  leaves  port  in 
the  afternoon,  her  position  worked  out  the  next  day  at  meridian 
would  be  short  of  24  hours,  and  would  be  called  a  short  day. 

In  sailing  east,  also,  the  ship  advances  to  meet  the  sun,  thus 
shortening  the  day,  while  the  opposite  effect  is  realized  in  sailing 
west.  (See  Circumnavigators'  Day.) 

MERC  A  TOR'S  SAILING.— When  seeking  to  compare  the 
meridional  difference  of  latitude  and  the  difference  of  longitude, 
if  the  figures  of  same  exceed  those  in  the  tables,  point  off  one  or 
more  places  so  as  to  reduce  them  to  the  table  limits,  and  this  will 
not  change  the  course-angle  because  you  point  off  as  much  of  one 
quantity  as  you  do  of  the  other.  If  the  proper  difference  of  lati- 
tude is  too  large  for  the  latitude  column,  point  off  one  place  or 
more ;  but  be  sure  to  multiply  the  figures  obtained  for  the  distance 
accordingly. 

MIDDLE  LATITUDE  SAILING— Strictly  speaking,  when 
the  course  of  the  ship  crosses  the  equator,  the  course  should  be 
worked  for  each  side  of  the  Line,  in  order  to  obtain  the  correct 
middle  latitude  for  use  in  converting  the  difference  of  longitude 
into  departure. 


150  THE  NAVIGATOR'S  POCKET-BOOK 

When  the  difference  of  latitude  and  the  departure  exceeds  the 
table  limits,  proceed  as  explained  in  this  ADDENDA  under  the  head 
of  Dead  Reckoning. 

SHORT  DAY.—  (See  LONG  DAY.) 

SUNRISE  AND  SUNSET.— The  apparent  time  of  sunrise 
and  sunset  is  found  in  the  azimuth  tables  published  by  the  United 
States  Navy  Department,  also  by  Burdwood  and  Davis,  for  va- 
rious latitudes  and  declinations  of  the  sun,  and  in  order  to  reduce 
this  time  to  mean,  or  shore  time,  it  is  necessary  to  apply  the  equation 
of  time  given  in  the  Nautical  Almanac  for  the  date  in  question. 

To  calculate  the  time  of  sunrise  and  sunset,  independent  of  azi- 
muth-table aid,  proceed  as  follows  :  Add  together  the  logarithms 
tangent  of  the  ship's  latitude  and  tangent  of  the  sun's  declination. 
The  result  will  be  the  logarithm  cosine  in  apparent  time,  and  if 
the  latitude  and  declination  are  of  different  names,  it  will  be  the 
apparent  time  of  sunset,  and  subtracted  from  12  hours  it  will  be 
the  apparent  time  of  sunrise.  If  the  latitude  and  declination  are 
of  the  same  name  the  cosine  time  will  be  the  apparent  time  of 
sunrise,  and  subtracted  from  12  hours  the  apparent  time  of  sun- 
set. To  convert  this  time  into  mean  time,  apply  the  equation  of 
time  for  the  given  date,  as  directed  in  the  Nautical  Almanac. 

It  is  to  be  understood  that  the  foregoing  rule  gives  the  time  of 
the  sun's  centre  on  the  horizon,  considering  the  observer's  eye  to 
be  at  the  level  of  the  sea,  and  without  being  influenced  by  refrac- 
tion. In  order  to  find  the  time  of  the  sun's  rising  and  setting  with 
the  refraction  and  dip  allowed  for,  add  together  the  logarithms 
secant  of  the  ship's  latitude,  secant  of  the  sun's  declination,  co- 
secant of  the  hour  angle  at  rising  or  setting,  and  the  sine  of  34' 
plus  the  dip  given  in  Table  14  for  the  height  of  the  observer's  eye 
above  the  sea  level.  The  sum  of  these  logarithms  is  the  log  sine  of 
the  small  portion  of  time  between  the  true  and  apparent  hour  angles, 
and  this  amount  must  be  applied  to  the  hour  angle  first  found. 

TIDES.— To  find  the  approximate  time  of  high  water  at  any 
place,  is  a  simple  calculation.  Select  from  the  Nautical  Al- 
manac the  time  of  the  moon's  meridian  passage  at  Greenwich 
and  correct  it  for  the  ship's  longitude  east  or  west  of  Greenwich 
by  the  use  of  Table  11.  Now,  to  this  time  of  the  moon's  passage 
over  the  meridian  of  the  ship  add  the  tide-hour  from  Tables  either 
46  or  47— the  first  for  places  on  the  coasts  of  the  United  States  and 
the  latter  for  foreign  coasts — and  the  answer  will  be  the  time  of 
'ligh  water  at  the  given  place. 


THE  NAVIGATOR'S  POCKET-BOOK          151 

TIME  INTO  ARC.— (See  Arc  into  Time.) 

TRUE  AZIMUTH  BY  LOGARITHMS.— Convert  the  ob- 
served altitude  into  a  true  altitude,  then  find  the  polar  distance. 
Next  add  together  the  polar  distance,  true  altitude  and  the  lati- 
tude by  dead  reckoning,  divide  their  sum  by  2,  and  call  the  result 
the  half  sum,  from  which  subtract  the  polar  distance,  and  note 
the  remainder.  Select  the  secant  of  the  true  altitude,  secant  of 
the  latitude,  cosine  of  the  half  sum,  and  cosine  of  the  remainder 
The  half  sum  of  these  four  logs  will  be  named  cosine,  and  the 
same  will  be  looked  for  in  Table  44.  The  degrees  and  minutes  oi 
arc  given  for  the  cosine — whether  found  from  top  or  bottom  of 
page — must  be  multiplied  by  2  to  obtain  the  true  azimuth. 

In  selecting  the  degrees  for  the  log  cosine,  whether  found  from 
the  top  or  bottom  of  page,  take  the  smallest  number  of  degrees, 
and  use  the  minute  column  belonging  to  same. 

TO  INTERPOLATE  SPECIAL  LOGARITHMS.— It  is  to 
be  explained  that  the  method  of  interpolation  by  inspection,  as 
explained  on  page  85,  is  not  available  in  that  portion  of  the  table 
where  the  logarithmic  differences  vary  so  rapidly  that  no  values 
will  apply  alike  to  all  the  angles  on  the  same  page,  therefore,  on 
such  pages  (for  example,  0°,  1°,  2°,  3°,  4°,  85°,  86°,  87°,  88°,  89°, 
90°,  91°,  92°,  93°,  94°,  175°,  176°,  177°,  178°,  and  179°),  the  differ- 
ence for  one  minute  is  given  in  a  column  headed  DIFF.  1'  instead 
of  the  usual  difference  for  each  second.  In  these  cases  the  inter- 
polation must  be  made  by  computation.  The  column  difference 
for  1'  must  be  divided  by  60  to  get  the  figures  for  1",  then  these 
figures  must  be  multiplied  by  the  number  of  seconds  of  the  angle 
to  obtain  the  correction,  and  this  will  be  applied  as  heretofore 
directed  on  page  85.  When  using  the  left  hand  minute  column 
of  the  table,  the  DIFF.  FOR  1'  will  be  selected  directly  opposite 
the  minutes  of  the  angle  ;  but  when  using  the  right  hand  minute 
column,  the  DIFF.  FOR  1'  will  be  selected  from  the  line  next  above 
the  minutes  of  the  angle. 

TO  SUBSTITUTE  TABLE  27.— Bowditch  having  substi- 
tuted a  new  and  less  desirable  Table  27,  a  reprint  of  the  old  one, 
under  the  caption  of  Square  of  Time  Table,  has  been  added  in 
the  back  of  this  book  for  the  benefit  of  the  navigator. 


152 


THE   NAVIGATORS    POCKET-BOOK 


PATTERSON'S  TABLE  OP  CORRECTION 

19O7-1908                            TO  BE  APPLIED  TO  THE                           1909-191O 

TRUE   ALTITUDE   OF   THE   POLAR  STAR. 

R.  A.  of 
Meridian. 

Alt.  Cor- 
rection. 

R.  A.  of 

Meridian. 

Alt.  Cor- 
rection. 

Meridian. 

rection. 

Meridian. 

rection. 

h.  m. 

o       / 

h.    m. 

e      / 

h.   m. 

o       / 

h.    m. 

0         / 

0      0 

-1      06 

6    10 

-0    22 

12    10 

4-       06 

18     10 

4-0    24 

0    10 

-1    06 

6    20 

-0    19 

12    20 

4-       07 

18    20 

4-0    21 

0    20 

-1     07 

6    30 

-0    16 

12    30 

+       08 

18    30 

4-0    18 

0    30 

-1    08 

6    40 

-0    13 

12    40 

4-       08 

18    40 

4-0    15 

0    40 

-       08 

6    50 

-0    10 

12    50 

4-       09 

18    50 

+  0    12 

0    50 

-       09 

7    00 

-0    07 

13    00 

4-       10 

19    00 

4-0    09 

00 

-       10 

7    10 

-0    03 

13    10 

4-         10 

19    10 

+  0    06 

10 

-       10 

7    20 

0    00 

13    20 

+         11 

19    20 

4-0    03 

20 

-       11 

7    30 

+  0    02 

13    30 

4-         11 

19    30 

0    00 

30 

11 

7    40 

+  0    05 

13    40 

4-         11 

19    40 

-0    03 

40 

-       11 

7    50 

-f-0    08 

13    50 

4-         10 

19    50 

-0    06 

50 

-       11 

8    00 

+  0    11 

14    00 

4-         10 

20    00 

-0    10 

2    00 

-       10 

8    10 

+  0    15 

14     10 

4-         10 

20    10 

-0    13 

2    10 

10 

8    20 

-»-0    18 

14    20 

4-         09 

20    20 

—  0    16 

2    20 

-       09 

8    30 

+  0    20 

14    30 

+       08 

20    30 

-0    19 

2    30 

-       08 

8    40 

+  0    23 

14    40 

+       07 

20    40 

-0    22 

2    40 

-       07 

8    50 

+  0    26 

14    50 

4-       07 

20    50 

-0    25 

2    50 

-       06 

9    00 

+  0    29 

15    00 

4-       05 

21     00 

-0    28 

3    00 

—  1    05 

9    10 

+  0    32 

15    10 

+  1    04 

21     10 

-0    30 

3    10 

-1    04 

9    20 

+  0    35 

15    20 

4-  1    03 

21    20 

-0    33 

3    20 

-1    02 

9    30 

+  0    37 

15    30 

4-  1    01 

21    30 

-0    36 

3    30 

-1    01 

9    40 

4-0    40 

15    40 

4-0    59 

21     40 

-0    39 

3    40 

-0    59 

9    50 

+  0    42 

15    50 

4-0    58 

21    50 

-0    41 

3    50 

-0    58 

10    00 

+  0    45 

16    00 

4-0    56 

22    00 

-0    44 

4    00 

-0    55 

10    10 

+  0    47 

16    10 

+  0    54 

22    10 

-0    46 

4    10 

-0    53 

10    20 

4-0    49 

16    20 

4-0    52 

22    20 

-0    48 

4    20 

-0    51 

10    30 

4-0    51 

16    30 

4-  0    50 

22    30 

-0    51 

4    30 

-0    48 

10    40 

4-0    54 

16    40 

4-0    48 

22    40 

-0    53 

4    40 

-0    46 

10    50 

+  0    55 

16    50 

4-0    45 

22    50 

-0    55 

4    50 

-0    43 

11    00 

4-0    57 

17    00 

4-0    43 

23    00 

-0    57 

1    5    00 

-0    41 

11     10 

4-0    59 

17    10 

4-0    40 

23    10 

-0    59 

5     10 

-0    38 

11     20 

+  1    01 

17    20 

4-0    38 

23    20 

-1    00 

5    20 

-0    36 

11    30 

4-1    03 

17    30 

+  0    35 

23    30 

-1    03 

5    30 

-0    34 

11    40 

+  1    04 

17    40 

4-0    32 

23    40 

-1    03 

5    40 

-0    31 

11    50 

4-  1    05 

17    50 

4-0    30 

23    50 

-  1    06 

5    50 

-0    28 

12    00 

4-  1    06 

18    00 

+  0    27 

24    00 

-1    06 

6    00 

—  0    25 

#     * 

*       * 

THE  NAVIGATOR'S  POCKET-BOOK 


153 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Yards. 

Height  of  Light  Above  Sea-Level. 

30  Feet. 

35  Feet 

40  Feet. 

45  Feet. 

100  

Off/ 

5  42  40 
3  48  50 
2  51  40 
2  17  30 
1  54  30 

Of// 

6  39  20 
4  26  50 
3  20  20 
2  40  20 
2  13  40 

of// 

7  35  40 
5  04  50 
3  48  50 
3  03  10 
2  32  40 

Of// 

8  31  50 
5  42  40 
4  17  20 
3  26  00 
2  51  40 

150  

200  

250  

300  

350  

1  38  10 
1  26  00 
1  16  20 
1  08  40 
1  02  30 

1  54  30 
1  40  10 
1  29  10 
1  20  10 
1  12  50 

2  10  50 
1  54  30 
1  41  50 
1  31  40 
1  23  20 

2  17  10 
2  08  50 
1  54  30 
1  43  10 
1  33  40 

400  

450  

500  (J  m.). 
550  

600  

0  57  20 
0  52  50 
0  49  10 
0  45  50 
0  43  00 

1  06  50 
1  01  40 
0  57  20 
0  53  30 
0  50  10 

1  16  20 
1  10  30 
1  05  30 
1  01  10 

0  57  20 

1  26  00 
1  19  20 
1  13  40 
1  08  40 
1  04  30 

650     

700  

750  

800  

850  

0  40  30 
0  38  10 
0  36  10 
0  34  20 

0  47  10 
0  44  30 
0  42  10 
0  40  10 

0  53  50 
0  51  00 
0  48  10 
0  45  50 

1  00  40 
0  57  20 
0  54  20 
0  51  30 

900  

950  

1000  (Jm.) 

154 


THE  NAVIGATOR'S  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Yards. 

Height  of  Light  Above  Sea-Level. 

30  Feet. 

35  Feet. 

40  Feet. 

45  Feet. 

1050  

o     f      n 

0  32  40 
0  31  10 
0  29  50 
0  28  40 
0  27  30 

o     /      // 

0  38  10 
0  36  30 
0  34  50 
0  33  20 
0  32  00 

0       /         // 

0  43  40 
0  41  40 
0  39  50 
0  38  10 
0  36  40 

0       /        // 

0  49  10 
0  46  50 
0  44  50 
0  43  00 
0  41  10 

1100  

1150  

1200  

1250  

1300  

0  26  30 
0  25  30 
0  24  30 
0  23  40 
0  22  50 

0  30  50 
0  29  00 
0  28  40 
0  27  40 
0  26  40 

0  35  20 
0  34  00 
0  32  40 
0  31  40 
0  30  30 

0  39  40 
0  38  10 
0  36  50 
0  35  30 
0  34  20 

1350  

1400  

1450  

1500  (f  m.) 

1550  

0  22  10 
0  21  30 
0  20  50 
0  20  10 
0  19  40 

0  25  50 
0  25  00 
0  24  20 
0  23  30 
0  22  50 

0  29  30 

0  28  40 
0  27  50 
0  27  00 
0  26  10 

0  33  20 
0  32  10 
0  31  10 
0  30  20 
0  29  30 

1600  

1650  

1700  

1750  

1800  

0  19  10 
0  18  30 
0  18  10 
0  17  40 
0  17  10 

0  22  20 
0  21  40 
0  21  10 
0  20  30 
0  20  00 

0  25  30 
0  24  50 
0  24  10 
0  23  30 
0  22  50 

0  28  40 
0  27  50 
0  27  10 
0  26  30 
0  25  50 

1850  

1900  

1950  

2000  (1m.) 

THE  NAVIGATOR'S  POCKET-BOOK 


155 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea  Level. 

50  Feet. 

55  Feet. 

60  Feet. 

65  Feet. 

0.1.. 

o      /        // 

4  45  50 
2  23  10 
1  35  30 
1  11  40 

0  57  20 

o      /       // 

5  14  10 
2  37  30 
1  45  00 
1  18  50 
1  03  00 

Of// 

5  42  40 
2  51  40 
1  54  30 
1  26  00 
1  08  40 

o      /       // 

6  11  00 
3  06  00 
2  04  00 
1  33  00 
1  14  30 

0.2  

0.3  

0.4  

0.5  

0.6  

0  47  40 
0  40  50 
0  35  50 
0  31  50 
0  28  40 

0  52  30 
0  45  00 
0  39  20 
0  35  00 
0  31  30 

0  57  20 
0  49  10 
0  43  00 
0  38  10 
0  34  20 

1  02  00 
0  53  10 
0  46  30 
0  41  20 
0  37  10 

0.7  

0.8  

0.9  

1.0  

1.1  

0  26  00 
0  24  00 
0  22  00 
0  20  30 
0  19  10 

0  28  40 
0  26  20 
0  24  10 
0  22  30 
0  21  00 

0  31  10 
0  28  40 
0  26  30 
0  24  30 
0  22  50 

0  34  00 
0  31  00 
0  28  40 
0  26  40 
0  24  50 

1.2  

1.3  

1.4  

1.5  

1.6.,  

0  17  50 
0  16  50 
0  15  50 
0  15  00 
0  14  20 

0  19  40 
0  18  30 
0  17  30 
0  16  30 
0  15  40 

0  21  30 
0  20  10 
0  19  10 
0  18  10 
0  17  10 

0  23  20 
0  21  50 
0  20  40 
0  19  40 
0  18  40 

1.7  

1.8  

1.9  

2.0  

156 


THE   NAVIGATOR  S*  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

70  Feet. 

75  Feet. 

80  Feet. 

85  Feet. 

0.1  

O          /        It 

6  39  20 
3  20  20 
2  13  40 
1  40  10 
1  20  10 

O           /        ft 

7  07  30 
3  34  30 
2  23  10 
1  47  20 
1  26  00 

o        /      // 

7  35  40 
3  48  50 
2  32  40 
1  54  30 
1  31  40 

O           /        // 

8  03  50 
4  03  10 
2  42  10 
2  01  40 
1  37  20 

0.2  

0.3  

0.4  

0.5  

0.6  

1  06  50 
0  57  20 
0  50  10 
0  44  30 
0  40  10 

1  11  40 
1  01  20 
0  53  40 
0  47  40 
0  43  00 

1  16  20 
1  05  30 

0  57  20 
0  51  00 
0  45  50 

1  21  10 
1  09  30 
1  00  50 
0  54  10 
0  48  40 

0.7  

0.8  

0.9  

1.0  

1.1  

0  36  30 
0  33  20 
0  30  50 

0  28  40 
0  26  40 

0  39  00 
0  35  50 
0  33  00 
0  30  40 
0  28  40 

0  41  40 
0  38  10 
0  35  10 
0  32  40 
0  30  30 

0  44  20 
0  40  30 
0  37  30 
0  34  50 
0  32  30 

1.2....... 

13.... 

1.4  

1.5  

1.6  

0  25  00 
0  23  40 
0  22  20 
0  21  10 
0  20  00 

0  26  50 
0  25  20 
0  23  50 

0  22  40 
0  21  30 

0  28  40 
0  28  00 
0  25  30 
0  24  10 
0  22  50 

0  30  30 
0  28  40 
0  27  00 
0  25  40 
0  24  20 

1.7  

1.8  

1.9  

2.O.. 

THE  NAVIGATOR'S  POCKET-BOOK 


15? 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

70  Feet. 

75  Feet. 

80  Feet. 

85  Feet. 

2.1 

0        /          // 

0  19  10 
0  18  10 
0  17  30 
0  16  40 
0  16  00 

0  20  30 
0  19  30 
0  18  40 
0  17  50 
0  17  10 

0  21  50 
0  20  50 
0  20  00 
0  19  10 
0  18  20 

0  23  10 
0  22  10 
0  21  10 
0  20  20 
0  19  30 

2.2  

2.3  

2.4  

2.5  

2.6.., 

0  15  20 
0  14  50 
0  14  20 
0  13  50 
0  13  20 

0  16  30 
0  15  50 
0  15  20 
0  14  50 
0  14  20 

0  17  40 
0  17  00 
0  16  20 
0  15  50 
0  15  20 

0  18  40 
0  18  00 
0  17  20 
0  16  50 
0  16  10 

2.7  

2.8  

2.9  

3.0  

3.1  

0  13  00 
0  12  30 
0  12  10 
0  11  50 
0  11  30 

0  14  00 
0  13  30 
0  13  00 
0  12  40 
0  12  20 

0  14  50 
0  14  20 
0  13  50 
0  13  30 
0  13  10 

0  15  40 
0  15  10 
0  14  50 
0  14  20 
0  13  50 

3.2  

3.3  

3.4  

3.5  

3.6  

0  11  10 
0  10  50 
0  10  30 
0  10  20 
0  10  00 

0  12  00 
0  11  40 
0  11  20 
0  11  00 
0  10  40 

0  12  40 
0  12  20 
0  12  00 
0  11  40 
0  11  30 

0  13  20 
0  13  10 
0  12  50 
0  12  30 
0  12  10 

3.7  

3.8  

3.9  

4.0  

158 


THE  NAVIGATOR'S-  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

90  Feet, 

95  Feet. 

100  Feet. 

105  Feet. 

0.1  

o      r      tt 

8  31  50 
4  17  20 
2  51  40 
2  OS  50 
1  43  10 

Q      r      it 

8  59  50 
4  31  30 
3  01  20 
2  25  00 
1  48  50 

0  /  // 

9  27  40 
4  45  50 
3  10  50 
2  23  10 
1  54  30 

o  /  n 

9  55  30 
5  00  00 
3  20  20 
2  30  20 
2  00  20 

0.2  

0.3.      ..    . 

0.4. 

0.5  

0.6   

1  26  00 
1  13  40 
1  04  30 
0  57  20 
0  51  30 

1  30  40 
1  17  40 
1  08  00 
1  00  30 
0  54  30 

1  35  30 
1  21  50 
1  11  40 
1  03  40 

0  57  20 

1  40  10 
1  26  00 
1  15  10 
1  06  50 
1  00  10 

0.7  

08  

0.9  

1.0  

1.1  

0  46  50 
0  43  00 
0  39  40 
0  36  50 
0  34  20 

0  49  30 
0  45  20 
0  41  50 
0  38  50 
0  36  20 

0  52  00 

0  47  40 
0  44  00 
0  40  50 
0  38  10 

0  54  40 
0  50  10 
0  46  20 
0  43  00 
0  40  10 

1.2  

1.3  

1.4  

1.5  

1.6   

0  32  10 
0  30  20 
0  28  40 
0  27  10 
0  25  50 

0  34  00 
0  32  00 
0  30  10 
0  28  40 

0  27  10 

0  35  50 
0  33  40 
0  31  50 
0  30  10 
0  28  40 

0  37  40 
0  35  20 
0  33  20 
0  31  40 
0  30  00 

1.7  

1.8  

1.9  

2.0  

THE  NAVIGATOR'S  POCKET-BOOK 


PATTERSON'S  DANGER-  ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-  Level. 

90  Feet. 

95  Feet. 

100  Feet. 

105  Feet. 

2.1  

o      /       n 

0  24  30 
0  23  30 
0  22  20 
0  21  30 
0  20  40 

Q        t          If 

0  25  50 
0  24  40 
0  23  40 
0  22  40 
0  21  50 

0  /  // 

0  27  20 
0  26  00 
0  24  50 
0  23  50 
0  22  50 

0  /  // 

0  28  40 
0  27  20 
0  26  10 
0  25  00 
0  24  00 

2.2  

2.3  

2.4  

2.5  

2.6-  

0  19  50 
0  19  10 
0  18  20 
0  17  50 
0  17  10 

0  21  00 
0  20  10 
0  19  30 
0  18  50 
0  18  10 

0  22  00 
0  21  10 
0  20  30 
0  19  40 
0  19  10 

0  23  10 
0  22  20 
0  21  30 
0  20  40 
0  20  00 

2.7  

2.8  

2.9  

3.0  

3.1  

0  16  40 
0  16  10 
0  15  40 
0  15  10 
0  14  40 

0  17  30 
0  17  00 
0  16  30 
0  16  00 
0  15  30 

0  18  30 
0  17  50 
0  17  20 
0  16  50 
0  16  20 

0  19  20 
0  18  50 
0  18  10 
0  17  40 
0  17  10 

3.2  

3.3  

3.4  

3.5  

3.6.. 

0  14  20 
0  14  00 
0  13  30 
0  13  10 
0  12  50 

0  15  10 
0  14  40 
0  14  20 
0  14  00 
0  13  40 

0  15  50 
0  15  30 
0  15  00 
0  14  40 
0  14  20 

0  16  40 
0  16  10 
0  15  50 
0  15  20 
0  15  00 

3.7  

3.8  

3.9   

4.0  

160 


THE   NAVIGATOR  $   POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

110  Feet. 

115  Feet. 

120  Feet. 

125  Feet. 

0.1  

0         /         // 

10  23  20 
5  14  10 
3  29  50 
2  37  30 
2  06  00 

10  51  00 
5  28  30 
3  39  20 
2  44  40 
2  11  40 

11  18  40 
5  42  40 
3  48  50 
2  51  40 
2  17  30 

11  46  10 
5  56  50 
3  58  20 
2  58  50 
2  23  10 

0.2  

0.3   

0.4  

0.5  

0.6....... 

1  45  00 
1  30  00 
1  18  50 
1  10  00 
1  03  00 

1  49  50 
1  34  10 
1  22  20 
1  13  10 
1  05  50 

1  54  30 
1  38  10 
1  26  00 
1  16  20 
1  08  40 

1  59  20 
1  42  20 
1  29  30 
1  19  30 
1  11  40 

0.7  

0.8  

0.9  

1.0  

1.1  

0  67  20 
0  52  30 
0  48  30 
0  45  00 
0  42  00 

0  59  50 
0  54  50 
0  50  40 
0  47  00 
0  44  00 

1  02  30 
0  57  20 
0  52  50 
0  49  10 
0  45  50 

1  05  10 
0  59  40 
0  55  00 
0  51  10 

0  47  40 

1.2  

1.3  

1.4  

1.5  

1.6  

0  39  20 
0  37  00 
0  35  00 
0  33  10 
0  31  30 

0  41  10 
0  38  50 
0  36  40 
0  34  40 
0  33  00 

0  43  00 
0  40  30 
0  38  10 
0  36  10 
0  34  20 

0  44  50 
0  42  10 
0  39  50 
0  37  40 
0  35  50 

1.7  

1.8  

1.9  

2.O.. 

THE  NAVIGATOR'S  POCKET-BOOK 


161 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

110  Feet. 

115  Feet. 

120  Feet. 

125  Feet. 

2.1  

0  30  00 
0  28  40 
0  27  20 
0  26  20 
0  25  10 

0  31  20 
0  30  00 

0  28  40 
0  27  30 
0  26  20 

0  32  40 
0  31  10 
0  29  50 
0  28  40 

0  27  30 

0  34  10 
0  32  30 
0  31  10 
0  29  50 
0  28  40 

2.2     ..    .. 

2  3  

2.4  

2.5  

2.6  

0  24  10 
0  23  20 
0  22  30 
0  21  40 
0  21  00 

0  25  20 
0  24  20 
0  23  30 
0  22  40 
0  22  00 

0  26  30 
0  25  30 
0  24  30 
0  23  40 
0  22  50 

0  27  30 
0  26  30 
0  25  30 
0  24  40 
0  23  50 

2.7  

2.8  

2.9  

3.0  

3.1  

0  20  20 
0  19  40 
0  19  10 
0  18  30 
0  18  00 

0  21  10 
0  20  30 
0  20  00 
0  19  20 
0  18  50 

0  22  10 
0  21  30 
0  20  50 
0  20  10 
0  19  40 

0  23  10 
0  22  20 
0  21  40 
0  21  00 
0  20  30 

3.2  

3.3  

3.4  

3.5  

3.6  

0  17  30 
0  17  00 
0  16  30 
0  16  10 
0  15  40 

0  18  20 
0  17  50 
0  17  20 
0  16  50 
0  16  30 

0  19  10 
0  18  30 
0  18  10 
0  17  40 

0  17  10 

0  19  50 
0  19  20 
0  18  50 
0  18  20 
0  17  50 

37 

3.8  

3.9  

4.0  

162 


THE   NAVIGATOK^   POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

130  Feet. 

135  Feet. 

140  Feet. 

145  Feet. 

0.1  

0        /         // 

12  13  30 
6  11  00 

4  07  50 
3  06  00 
2  28  50 

o  /  n 

12  40  50 
6  25  10 
4  17  20 
3  13  10 
2  34  40 

0  /  // 

13  08  00 
6  39  20 
4  26  50 
3  20  20 
2  40  20 

o  /  // 

13  35  10 
6  53  20 
4  36  20 
3  27  30 
2  46  00 

0.2  
0.3  

0.4  

0.5  

0.6  

2  04  00 
1  46  20 
1  33  00 
1  22  40 
1  14  30 

2  08  50 
1  50  30 
1  36  40 
1  26  00 
1  17  20 

2  13  40 
1  54  30 
1  40  10 
1  29  10 
1  20  10 

2  18  20 
1  58  40 
1  43  50 
1  32  20 
1  23  00 

0.7  

0.8  

0  9,    .    ... 

1.0  

1.1  

1  07  40 
1  02  00 
0  57  20 
0  53  10 
0  49  40 

1  10  20 
1  04  30 
0  59  30 
0  55  10 
0  51  30 

1  12  50 
1  06  50 
1  01  40 
0  57  20 
0  53  30 

1  15  30 
1  09  10 
1  03  50 
0  59  20 
0  55  20 

1.2  

1.3  

1.4  

1.5  

1.6  

0  46  30 
0  43  50 
0  41  20 
0  39  10 
0  37  10 

0  48  20 
0  45  30 
0  43  00 
0  40  40 

0  38  40 

0  50  10 
0  47  10 
0  44  30 
0  42  10 
0  40  10 

0  51  50 
0  48  50 
0  46  10 
0  43  40 
0  41  30 

1.7  

1.8  

1.9  

2.0  

SHE  JSAVIGATOR'S  POCKET-SOOK 


163 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

130  Feet. 

135  Feet. 

140  Feet. 

145  Feet. 

2.1  

o      f       ft 

0  35  30 
0  33  50 
0  32  20 
0  31  00 
0  29  50 

o  /  // 

0  36  50 
0  35  10 
0  33  40 
0  32  10 
0  31  00 

O  f  H 

0  38  10 
0  36  30 
0  34  50 
0  33  20 
0  32  00 

o  /  // 

0  39  30 
0  37  50 
0  36  10 
0  34  40 
0  33  10 

2.2  

2.3  

2  4  

2.5  

2.6  

0  28  40 
0  27  30 
0  26  40 
0  25  40 
0  24  50 

0  29  40 

0  28  40 
0  27  40 
0  26  40 
0  25  50 

0  30  50 
0  29  40 
0  28  40 
0  27  40 
0  26  50 

0  32  00 
0  30  50 
0  29  40 
0  28  40 
0  27  40 

2.7  

2.8  

2  9  

3.0  

3.1  

0  24  00 
0  23  20 
0  22  30 
0  21  50 
0  21  20 

0  25  00 
0  24  10 
0  23  30 
0  22  40 
0  22  10 

0  25  50 
0  25  00 
0  24  20 
0  23  30 

0  22  50 

0  26  50 
0  26  00 
0  25  10 
0  24  30 
0  23  40 

3.2  

3.3  

3  4  

3.5  

3.6  

0  20  40 
0  20  10 
0  19  40 
0  19  10 
0  18  40 

0  21  30 
0  20  50 
0  20  20 
0  19  50 
0  19  20 

0  22  20 
0  21  40 
0  21  10 
0  20  30 
0  20  00 

0  23  00 
0  22  30 
0  21  50 
0  21  20 
0  20  50 

3.7  

3.8  

3.9  

4.0  

164 


THE   NAVIGATOR. S   POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

150  Feet. 

155  Feet. 

160  Feet. 

165  Feet. 

0  1  

o      /      // 

14  02  10 
7  07  30 
4  45  50 
3  34  30 
2  51  40 

o  /  /r 

14  29  00 
7  21  40 
4  55  20 
3  41  40 

2  57  30 

0  /  // 

14  55  50 
7  35  40 
5  04  50 
3  48  50 
3  03  10 

o  /  ft 

15  22  30 
7  49  40 
5  14  10 
3  56  00 
3  08  50 

0.2  

0.3  

0.4  

0.5  

0  6  

2  23  10 
2  02  40 
1  47  20 
1  35  30 
1  26  00 

2  27  50 
2  06  50 
1  51  00 
1  38  40 
1  28  50 

2  32  40 
2  10  50 
1  54  30 
1  41  50 
1  31  40 

2  37  30 
2  15  00 
1  58  10 
1  45  00 
1  34  30 

0.7  

0.8   

0  9  

1.0  

1.1  

1  18  10 
1  11  40 
1  06  10 
1  01  20 

0  57  20 

1  20  49 
1  14  00 
1  08  20 
1  03  30 
0  59  10 

1  23  20 
1  16  20 
1  10  30 
1  05  30 
1  01  10 

1  26  00 
1  18  50 
1  12  40 
1  07  30 
1  03  00 

1.2  

1.3  

1.4  

1.5  

1.6  

0  53  40 
0  50  30 
0  47  40 
0  45  10 
0  43  00 

0  55  30 
0  52  10 
0  49  20 
0  46  40 
0  44  20 

0  57  20 
0  53  50 
0  51  00 
0  48  10 
0  45  50 

0  59  00 
0  55  40 
0  52  30 
0  49  40 
0  47  20 

1.7  

1.8  

1.9  

2.0  

THE  NAVIGATOR'S  POCKET-BOOK 


165 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

150  Feet. 

155  Feet. 

160  Feet. 

165  Feet. 

2.1  

0         /          // 

0  40  50 
0  39  00 
0  37  20 
0  35  50 
0  34  20 

o  f  n 

0  42  20 
0  40  20 
0  38  40 
0  37  00 
0  35  30 

0  /  // 

0  43  40 
0  41  40 
0  39  50 
0  38  10 
0  36  40 

0  f  // 

0  45  00 
0  43  00 
0  41  10 
0  39  20 
0  37  50 

2  2  

2.3  

2.4  

2.5  

26       .... 

0  33  00 
0  31  50 
0  30  40 
0  29  40 
0  28  40 

0  34  10 
0  32  50 
0  31  40 
0  30  40 
0  29  40 

0  35  20 
0  34  00 
0  32  40 
0  31  40 
0  30  30 

0  36  20 
0  35  00 
0  33  50 
0  32  40 
0  31  30 

2.7  

2.8  

2.9  

3.0  

3.1  

0  27  40 
0  26  50 
0  26  00 
0  25  20 
0  24  30 

0  28  40 
0  27  40 
0  26  50 
0  26  10 
0  25  20 

0  29  30 
0  28  40 
0  27  50 
0  27  00 
0  26  10 

0  30  30 
0  29  30 
0  28  40 
0  27  50 
0  27  00 

3.2  

3.3  

3.4  

3.5  

3.6  

0  23  50 
0  23  10 
0  22  40 

0  22  00 
0  21  30 

0  24  40 
0  24  00 
0  23  20 
0  22  50 

0  22  10 

0  25  30 
0  24  50 
0  24  10 
0  23  30 
0  22  50 

0  26  20 
0  25  30 
0  24  50 
0  24  10 
0  23  40 

3  7  

3.8  

3.9  

4.O.. 

166 


THE  NAVIGATOR'S  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

170  Feet. 

175  Feet. 

180  Feet. 

185  Feet. 

0.1  

O        f         ff 

15  49  10 
8  03  50 
5  23  40 
4  03  10 
3  14  40 

Of// 

16  15  40 
8  17  50 
5  33  10 
4  10  10 
3  20  20 

Of// 

16  42  00 
8  31  50 
5  42  40 
4  17  20 
3  26  00 

Of// 

17  08  10 
8  45  50 
5  52  00 
4  24  30 
3  31  40 

0  2  

0.3  

0.4  

0.5  ... 

0.6  

2  42  10 
2  19  00 
2  01  40 
1  48  10 
1  37  20 

2  47  00 
2  23  10 
2  05  20 
1  51  20 
1  40  10 

2  51  40 
2  27  10 
2  08  50 
1  54  30 
1  43  10 

2  56  30 
2  31  20 
2  12  30 
1  57  40 
1  46  00 

0.7  

0.8  

0.9  

1.0  

1.1  

1  28  30 
1  21  10 
1  14  50 
1  09  30 
1  05  00 

1  31  10 
1  23  30 
1  17  10 
1  11  40 
1  06  50 

1  33  40 
1  26  00 
1  19  20 
1  13  40 
1  08  40 

1  36  20 
1  28  20 
1  21  30 
1  15  40 
1  10  40 

1.2  

1.3  

1.4  

1.5  

1.6  

1  00  50 
0  57  20 
0  54  10 
0  51  20 

0  48  40 

1  02  40 
0  59  00 
0  55  40 
0  52  50 
0  50  10 

1  04  30 
1  00  40 
0  57  20 
0  54  20 
0  51  30 

1  06  10 
1  02  20 
0  58  50 
0  55  50 
0  53  00 

1.7  

1  8  

1.9  

2.0  

THE  NAVIGATOR'S  POCKET-BOOK 


167 


PATTERSON'S  DANGER-ANGLE  TABLES, 

Distance  in 
Miles 
and  Tenths* 

Height  of  Light  Above  Sea-Level. 

170  Feet. 

175  Feet 

180  Feet. 

185  Feet 

2.1  

o     /      n 

0  46  20 
0  44  20 

0  42  20 
0  40  30 
0  39  00 

o  /  n 

0  47  40 
0  45  30 
0  43  40 
0  41  50 
0  40  10 

Of// 

0  49  10 
0  46  50 
0  44  50 
0  43  00 
0  41  10 

o  /  // 

0  50  30 

0  48  10 
0  46  00 
0  44  10 
0  42  20 

2.2  

2.3  

2.4  

2.5  

2.6  

0  37  30 
0  36  00 
0  34  50 
0  33  30 
0  32  30 

0  38  30 
0  37  10 
0  35  50 
0  34  30 
0  33  20 

0  39  40 
0  38  10 
0  36  50 
0  35  30 
0  34  20 

0  40  50 
0  39  10 
0  37  50 
0  36  30 
0  35  20 

2.7  

2.8  

2.9  

3.0  

3.1  

0  31  20 
0  30  30 
0  29  30 
0  28  40 
0  27  50 

0  32  20 
0  31  20 
0  30  20 
0  29  30 

0  28  40 

0  33  20 
0  32  10 
0  31  10 
0  30  20 
0  29  30 

0  34  10 
0  33  10 
0  32  10 
0  31  10 
0  30  20 

3.2  

33  

3.4  

3.5  

3.6,  

0  27  00 
0  26  20 
0  25  40 
0  25  00 
0  24  20 

0  27  50 
0  27  10 
0  26  20 
0  25  40 
0  25  00 

0  28  40 
0  27  50 
0  27  10 
0  26  30 
0  25  50 

0  29  30 

0  28  40 
0  27  50 
0  27  10 
0  26  30 

307.o  

3.8  

3.9  ... 

4.0  

1G8 


THE   NAVIGATOR-6   POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-  Level. 

190  Feet. 

195  Feet. 

200  Feet 

205  Feet 

0.1.,  

o     /      n 

17  34  20 
8  59  50 
6  01  30 
4  31  30 
3  37  30 

o  /  // 

18  00  10 
9  13  50 
6  11  00 
4  38  40 
3  43  10 

O  /  H 

18  26  10 
9  27  40 
6  20  20 
4  45  50 
3  48  50 

Of// 

18  51  50 
9  41  40 
6  29  50 
4  53  00 
3  54  30 

0.2  

0.3  

0.4  

0.5  

0.6  

3  01  20 
2  35  20 
2  16  00 
2  00  50 
1  48  50 

3  06  00 
2  39  30 
2  19  30 
2  04  00 
1  51  40 

3  10  50 
2  43  30 
2  23  10 
2  07  20 
1  45  30 

3  15  30 
2  47  40 
2  26  40 
2  10  30 
1  57  20 

0.7  

0.8  

0.9  

1.0  

1.1  

1  39  00 
1  30  40 
1  23  40 
1  17  40 
1  12  30 

1  41  30 
1  33  00 
1  26  00 
1  19  50 
1  14  30 

1  44  10 
1  35  30 
1  28  10 
1  21  50 
1  16  20 

1  46  40 
1  37  50 
1  30  20 
1  23  50 
1  18  20 

1.2  

1.3  

1.4  

1.5  

1  6  

1  08  00 
1  04  00 
1  00  30 
0  57  20 
0  54  30 

1  09  50 
1  05  40 
1  02  00 
0  58  50 
0  55  50 

1  11  40 
1  07  20 
1  03  40 
1  00  20 

0  57  20 

1  13  20 
1  09  00 
1  05  10 
1  01  50 
0  58  40 

1.7  

1.8  

1.9  

2.0  

THE  NAVIGATOK'S  POCKET-BOOK 


:169 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

190  Feet. 

195  Feet. 

200  Feet. 

205  Feet. 

2.1  

o      /       // 

0  51  50 
0  49  30 
0  47  20 
0  45  20 
0  43  30 

o  t  n 

0  53  10 

0  50  50 
0  48  30 
0  46  30 
0  44  40 

o  t  tr 

0  54  30 
0  52  00 
0  49  50 
0  47  40 
0  45  50 

o  /  // 

0  56  00 
0  53  20 
0  51  00 
0  49  00 

0  47  00 

2.2  

2.3  

2.4  

2.5  

2.6  

0  41  50 
0  40  20 
0  38  50 
0  37  30 
0  36  20 

0  43  00 
0  41  20 
0  39  50 
0  38  30 
0  37  10 

0  44  00 
0  42  30 
0  40  50 
0  39  30 
0  38  10 

0  45  10 
0  43  30 
0  42  00 
0  40  30 
0  39  10 

2.7  

2.8  

2  9  

3.0  

3.1  

0  35  10 
0  34  00 
0  33  00 
0  32  00 
0  31  10 

0  36  00 
0  34  50 
0  33  50 
0  32  50 
0  31  50 

0  37  00 
0  35  50 
0  34  40 
0  33  40 
0  32  40 

0  37  50 
0  36  40 
0  35  40 
0  34  30 
0  33  30 

3.2  

3.3  

3.4  

3.5  

3.6  

0  30  10 
0  29  20 
0  28  40 
0  27  50 
0  27  10 

0  31  00 
0  30  10 
0  29  20 
0  28  40 
0  28  00 

0  31  50 
0  31  00 
0  30  10 
0  29  20 
0  28  40 

0  32  40 
0  31  40 
0  30  50 
0  30  10 
0  29  20 

3.7  

3  8  

3.9  

4  0  

170 


THE   NAVIGATORS   POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

210  Feet. 

215  Feet. 

220  Feet. 

225  Feet. 

0.1  

Off/ 

19  17  20 
9  56  00 
6  39  20 
5  00  00 
4  00  10 

o      /      // 

19  42  50 
10  09  30 
6  48  40 
5  07  10 
4  06  00 

O        f         ff 

20  08  10 
10  23  20 
6  58  10 
5  14  10 
4  11  40 

o      /       // 

20  30  20 
10  37  10 
7  07  30 
5  21  20 
4  17  20 

0.2  

0.3  

0.4  

0.5  

0.6  

3  20  20 
2  51  40 
2  30  20 
2  13  40 
2  00  20 

3  25  00 
2  55  50 
2  33  50 
2  16  50 
2  03  10 

3  29  50 
2  59  50 
2  37  30 
2  20  00 
2  06  00 

3  34  30 
3  04  00 
2  41  00 
2  23  10 
2  08  50 

0.7  

0.8  

0.9  

1  o  

1.1  

1  49  20 
1  40  10 
1  32  30 
1  26  00 
1  20  10 

1  52  00 
1  42  40 
1  34  40 
1  28  00 
1  22  10 

1  54  30 
1  45  00 
1  37  00 
1  30  00 
1  24  00 

1  57  10 
1  47  20 
1  39  10 
1  32  00 
1  26  00 

1.2  

1.3  

1.4  

1.5  

1.6  

1  15  10 
1  10  50 
1  06  50 
1  03  20 
1  00  10 

1  17  00 
1  12  30 
1  08  30 
1  04  50 
1  01  30 

1  18  50 
1  14  10 
1  10  00 
1  06  20 
1  03  00 

1  20  30 
1  15  50 
1  11  40 
1  07  50 
1  04  30 

1.7  

1.8  

1.9  

2.0  

THE  NAVIGATOR'S  POCKET-BOOK 


171 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

210  Feet. 

215  Feet. 

220  Feet. 

225  Feet. 

2.1  

o       /      // 

0  57  20 
0  54  40 
0  52  20 
0  50  10 
0  48  10 

O  /  ft 

0  58  40 
0  56  00 
0  53  30 
0  51  20 
0  49  20 

0  /  // 

1  00  00 
0  57  20 
0  54  50 
0  52  30 
0  50  20 

o  /  n 

1  01  20 
0  58  40 
0  56  00 
0  53  40 
0  51  30 

2.2  

2.3  

2.4  

2.5  

2.6  

0  46  20 
0  44  30 
0  43  00 
0  41  30 
0  40  10 

0  47  20 
0  45  40 
0  44  00 
0  42  30 
0  41  00 

0  48  30 
0  46  40 
0  45  00 
0  43  30 

0  42  00 

0  49  30 
0  47  40 
0  46  00 
0  44  30 
0  43  00 

2.7  

2.8  

2.9  

3.0  

3.1  

0  38  50 
0  37  40 
0  36  30 
0  35  20 
0  34  20 

0  39  40 
0  38  30 
0  37  20 
0  36  10 
0  35  10 

0  40  40 
0  39  20 
0  38  10 
0  37  00 
0  36  00 

0  41  40 
0  40  20 
0  39  00 
0  37  50 
0  36  50 

3.2  

3.3  

3.4  

3.5  

3.6  

0  33  20 
0  32  30 
0  31  40 
0  30  50 
0  30  00 

0  34  10 
0  33  20 
0  32  20 
0  31  30 
0  30  50 

0  35  00 
0  34  00 
0  33  10 
0  32  20 
0  31  30 

0  35  50 
0  34  50 
0  33  50 
0  33  00 
0  32  10 

3.7  

3.8  

3.9  

4.0  

172 


THE  NAVIGATOR'S  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

230  Feet. 

235  Feet. 

240  Feet. 

245  Feet. 

0.1  

O         /         // 

20  58  20 
10  51  00 
7  16  50 
5  28  30 
4  23  00 

o      /      // 

21  23  20 
11  04  50 
7  26  20 
5  35  30 
4  28  40 

o      /      // 

21  48  00 
11  18  40 
7  35  40 
5  42  40 
4  34  30 

o       /       // 

22  12  40 
11  32  20 
7  45  00 
5  49  40 
4  40  10 

0.2  

0.3  

0.4  

0.5  

0.6  

3  39  20 
3  08  00 
2  44  40 
2  26  20 
2  11  40 

3  44  00 
3  12  10 
2  48  10 
2  29  30 
2  14  30 

3  48  50 
3  16  10 
2  51  40 
2  32  40 
2  17  30 

3  53  40 
3  20  20 
2  55  20 
2  35  50 
2  20  20 

0.7  

0.8     

0.9  

1.0  

1.1  

1  59  40 
1  49  50 
1  41  20 
1  34  10 

1  27  50 

2  02  20 
1  52  10 
1  43  30 
1  36  10 
1  29  40 

2  05  00 
1  54  30 
1  45  40 
1  38  10 
1  31  40 

2  07  30 
1  57  00 
1  48  00 
1  40  10 
1  33  30 

1.2  

1  3.. 

1.4  

1.5  

1.6  

1  22  20 

1  17  30 
1  13  10 
1  09  20 
1  05  50 

1  24  10 
1  19  10 
1  14  50 
1  10  50 
1  07  20 

1  26  00 
1  20  50 
1  16  20 
1  12  20 
1  08  40 

1  27  40 
1  22  30 
1  18  00 
1  13  50 
1  10  10 

1.7  

1.8  

1.9  

2.O.. 

THE   NAVIGATORS    POCKET-BOOK 


173 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

230  Feet. 

235  Feet. 

240  F*et. 

245  Feet. 

2.1  

o     t      it 

1  02  40 
0  59  50 
0  57  20 
0  54  50 
0  52  40 

O  /  /f 

1  04  10 
1  01  10 
0  58  30 
0  56  10 
0  53  50 

O  /  h 

1  05  30 
1  02  30 
0  59  50 
0  57  20 
0  55  00 

0  /  // 

1  06  50 
1  03  50 
1  01  00 
0  58  30 
0  56  10 

2.2  

23       

2.4  

2.5  

2.6  

0  50  40 
0  48  50 
0  47  00 
0  45  30 
0  43  50 

0  51  50 
0  49  50 
0  48  00 
0  46  30 
0  44  50 

0  52  50 
0  51  00 
0  49  10 
0  47  20 
0  45  50 

0  54  00 
0  52  00 
0  50  10 
0  48  20 
0  46  50 

2.7  

2.8  

2.9  

3.0  

3.1  

0  42  30 
0  41  10 
0  40  00 
0  38  40 
0  37  40 

0  43  30 
0  42  00 
0  40  50 
0  39  40 
0  38  30 

0  44  20 
0  43  00 
0  41  40 
0  40  30 
0  39  20 

0  45  20 
0  44  00 
0  42  30 
0  41  20 
0  40  10 

3.2  

3.3  

3.4  

3.5  

3.6  

0  36  40 
0  35  40 
0  34  40 
0  33  50 
0  33  00 

0  37  20 
0  36  20 
0  35  30 
0  34  30 
0  33  40 

0  38  10 
0  37  10 
0  36  10 
0  35  10 
0  34  20 

0  39  00 
0  38  00 
0  37  00 
0  36  00 
0  35  10 

3.7  

3.8  

3.9  

40.. 

174 


THE  NAVIGATOR'S  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

250  Feet, 

260  Feet. 

270  Feet. 

280  Feet. 

0.1  

0         /          // 

22  37  10 
11  46  10 
7  54  30 
5  56  50 
4  45  50 

0        /          // 

23  25  40 
12  13  30 
8  13  10 
6  11  00 

4  57  10 

0         /          // 

24  13  40 
12  40  50 
8  31  50 
6  25  10 
5  08  30 

o      f       n 

25  01  00 
13  08  00 
8  50  30 
6  39  20 
5  20  00 

0.2  

0.3  

0.4  

0.5  

0.6  

3  58  20 
3  24  20 
2  58  50 
2  39  00 
2  23  10 

4  07  50 
3  32  30 
3  06  00 
2  45  20 
2  28  50 

4  17  20 
3  40  40 
3  13  10 
2  51  40 
2  34  40 

4  26  50 
3  48  50 
3  20  20 
2  58  10 
2  40  20 

0.7  

0  8  

0.9  

1.0  

1.1  

2  10  10 
1  59  20 
1  50  10 
1  42  20 
1  35  30 

2  15  20 
2  04  10 
1  54  30 
1  46  20 
1  39  20 

2  20  30 
2  08  50 
1  59  00 
1  50  30 
1  43  10 

2  25  40 
2  13  40 
2  03  20 
1  54  30 
1  46  50 

1.2  

1.3..  

1.4  

1.5  

1.6  

1  29  30 
1  24  10 
1  19  30 
1  15  20 
1  11  40 

1  33  00 

1  27  40 
1  22  40 
1  18  20 
1  14  30 

1  36  40 
1  31  00 

1  26  00 
1  21  20 

1  17  20 

1  40  10 
1  34  20 
1  29  10 
1  24  30 
1  20  10 

1.7  

1.8  

1.9  

2.0  

THE  NAVIGATOR'S  POCKET-BOOK 


175 


PATTERSON'S  DANGER-  ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

250  Feet. 

260  Feet. 

270  Feet. 

280  Feet. 

2.1  

O  t  ft 

1  16  20 
1  12  50 
1  09  40 
1  06  50 
1  04  10 

1  08  10 
1  05  10 

1  02  20 
0  59  40 
0  57  20 

1  11  00 
1  07  40 
1  04  50 
1  02  00 
0  59  30 

1  13  40 
1  10  20 
1  07  10 
1  04  30 
1  01  50 

2.2  

2.3  

2.4  

2.5  

2.6  

0  55  00 
0  53  00 
0  51  10 
0  49  20 

0  47  40 

0  57  20 
0  55  10 
0  53  10 
0  51  20 
0  49  40 

0  59  30 
0  57  20 
0  55  10 
0  53  20 
0  51  30 

1  01  40 
0  59  20 
0  57  20 
0  55  20 
0  53  30 

2.7  

2.8  

2  9  

3.0  

3.1  

0  46  10 
0  44  50 
0  43  20 
0  42  10 
0  40  50 

0  48  00 
0  46  30 
0  45  10 
0  43  50 

0  42  30 

0  49  50 
0  48  20 
0  46  50 
0  45  30 
0  44  10 

0  51  40 
0  50  10 
0  48  40 
0  47  10 
0  45  50 

3.2  

3.3  

3.4  ... 

3.5  

3.6  

0  39  50 
0  38  40 
0  37  40 
0  36  40 
0  35  50 

0  41  20 
0  40  20 
0  39  10 
0  38  10 
0  37  10 

0  43  00 
0  41  50 
0  40  40 
0  39  40 
0  38  40 

0  44  30 
0  43  20 
0  42  10 
0  41  10 
0  40  10 

3.7  

3.8  

3.9  

4.0  

176 


THE  NAVIGATOR'S  POCKET-BOOK 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

290  Feet. 

300  Feet. 

310  Feet. 

320  Feet. 

0.1  

0         /            // 

27  45  30 
14  44  40 
9  57  00 
7  29  40 
6  00  30 

25  30  00 
13  24  50 
9  02  00 
6  48  00 
5  27  00 

26  15  50 
13  51  30 
9  20  20 
7  02  00 
5  38  10 

27  01  00 
14  18  10 
9  38  40 
7  15  50 
5  49  20 

0.2  

0.3  

0.4  

0.5   

0.6  

4  32  40 
3  53  50 
3  24  40 
3  02  00 
2  43  50 

4  42  00 
4  01  50 
3  31  50 
3  08  20 
2  49  30 

4  51  30 
4  10  00 
3  38  50 
3  14  30 
2  55  10 

5  00  50 
4  18  00 
3  45  50 
3  20  50 
3  00  50 

0.7  

0.8  

0.9  

1.0  

1.1  

2  29  00 
2  16  30 
2  06  00 
1  57  00 
1  49  20 

2  34  10 
2  21  20 
2  10  20 
2  01  10 
1  53  00 

2  39  10 
2  26  00 
2  14  50 
2  05  10 
1  56  50 

2  44  20 
2  30  40 
2  19  10 
2  09  10 
2  00  30 

1.2   

1.3  

1.4  

1  5  

1.6  

1  42  30 
1  36  30 
1  31  00 
1  26  20 
1  22  00 

1  46  00 
1  39  40 
1  34  10 
1  29  10 
1  24  50 

1  49  30 
1  43  00 
1  37  20 
1  32  10 

1  27  40 

1  53  00 
1  46  20 
1  40  30 
1  35  10 
1  30  30 

1.7  

1.8  

1.9  

2.0  

THE  NAVIGATOR'S  POCKET-BOOK 


177 


PATTERSON'S  DANGER-ANGLE  TABLES. 

Distance  in 
Miles 
and  Tenths. 

Height  of  Light  Above  Sea-Level. 

290  Feet. 

300  Feet. 

310  Feet. 

320  Feet. 

2.1  

o      /       // 

1  18  00 
1  14  30 
1  11  20 
1  08  20 
1  05  30 

o  /  // 

1  20  50 
1  17  00 
1  13  40 
1  10  40 
1  07  50 

o  /  // 

1  23  30 
1  19  40 
1  16  10 
1  13  00 
1  10  10 

o  /  tt 

1  26  10 
1  22  10 
1  18  40 
1  15  20 
1  12  20 

2.2     

2  3  

3.4  

2.5  

2.6  

1  03  00 
1  00  40 
0  58  30 
0  56  30 
0  54  40 

1  05  10 
1  02  50 
1  00  30 
0  58  30 
0  56  30 

1  07  20 
1  04  50 
1  02  40 
1  00  30 
0  58  20 

1  09  30 
1  07  00 
1  04  40 
1  02  20 
1  00  20 

2.7  

2.8  

2.9  

3.0  

3.1  

0  52  50 
0  51  10 
0  49  40 
0  48  10 
0  46  50 

0  54  40 
0  53  00 
0  51  20 
0  49  50 
0  48  30 

0  56  30 
0  54  50 
0  53  10 
0  51  30 
0  50  00 

0  58  20 
0  56  30 
0  54  50 
0  53  10 
0  51  40 

3.2  

3.3  

3.4  

3.5  

3.6  

0  45  30 
0  44  20 
0  43  10 
0  42  00 
0  41  00 

0  47  10 
0  45  50 
0  44  40 
0  43  30 
0  42  20 

0  48  40 
0  47  20 
0  46  10 
0  45  00 
0  43  50 

0  50  10 
0  48  50 
0  47  40 
0  46  20 
0  45  10 

3  7  

3.8  

3.9  

4.0  

12 


178 


THE  NAVIGATOR'S  POCKET-BOOK 


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THE  NAVIGATOR'S  POCKET-BOOK 


179 


PATTERSON'S  STAR  TABLES 


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180 


THE   NAVIGATOK  S   POCKET-BOOK 


TABLE  OP  DISTANCES 

AT  WHICH  OBJECTS  CAN  BE  SEEN  AT  SEA,  ACCORDING  TO 
THEIR  RESPECTIVE  ELEVATIONS  AND  THE  HEIGHT  OF  THE 
OBSERVER'S  EYE  ABOVE  SEA-LEVEL. 


Height 

Distance 

Height 

Distance 

Height 

Distance 

Height 

Distance 

in 

in  Nauti- 

in 

in  Nauti- 

in 

in  Nauti- 

in 

in  Nauti- 

Feet. 

cal  Miles. 

Feet. 

cal  Miles. 

Feet. 

cal  Miles. 

Feet. 

cal  Miles. 

5 

2.565 

55 

8.509 

110 

12.030 

450 

24.330 

10 

3.628 

60 

8.886 

120 

12.560 

500 

25.650 

15 

4.443 

65 

9.249 

130 

13  080 

550 

26.900 

20 

5.130 

70 

9.598 

140 

13.570 

600 

28.100 

25 

5  736 

75 

9.935 

150 

14.050 

650 

29.250 

30 

6.283 

80 

10.260 

200 

16.220 

700 

30.280 

35 

6.787 

85 

10.570 

250 

18.140 

800 

32.450 

40 

7.255 

90 

10.880 

300 

19.870 

900 

34.540 

45 

7.696 

95 

11.180 

350 

21  460 

1,000 

36.280 

50 

8.112 

100 

11  470 

400 

22.940 

* 

* 

Rule.— Add  together  the  figures  given  for  the  height  of  eye 
above  the  sea-level  and  the  figures  given  for  the  elevation  of  the 
object,  and  the  answer  will  be  the  distance  of  the  vessel  from 
the  object  in  question. 

When  a  low-lying  island,  or  shore,  or  the  hull  of  a  low-sided 
vessel  is  seen  awash  with  the  horizon,  the  distance  of  the  hori- 
zon for  the  height  of  the  observer's  eye  above  the  sea-level  will 
alone  give  the  distance  from  the  object. 

Example. — The  top  of  a  lighthouse  150  feet  high  is  seen 
awash  when  the  observer's  eye  is  15  feet  above  the  sea-level — 
required  the  distance  of  the  observer  from  the  light  ? 

Height  of  eye,      15  feet  =   4,443  miles. 
Height  of  light,  150  feet  =  14,050  miles. 

Distance  of  observer  from  light,  18,493  =  18|  miles  nearly. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


ASTRONOMY   LIBRARY 

DEC  1 4  1951 
MAR  2  0  1363 

CT5 


TABLE  27. 
To  reduce  the  number*  of  Table  26  to  othei  gw 

TA08G7 

3 

s. 

5 

Time  from  noon. 

•» 

1" 

J- 

jm 

4" 

5- 

6" 

r 

8* 

V* 

io- 

100.  0 

100.3 
100.7 

IOI   O 

101.3 

101,7 

11- 

14- 

o 
1 
t 
1 

4 
S 

0 

o 
1 

.  2 

4-0 
4-1 

4-J 

*3 
4-3 

9.0 

9-1 
9-  » 
9-3 
9.4 
9.5 

16.  o 
16.  i 
16.3 
16.4 
16.5 

-Sf 

16.9 

17.  1 

17  2 

"7-4 
•7  5 

25.0 

51! 
|j 

36.0 
36.2 
36.4 
36.6 
36.8 
37-0 

49  o 
49-2 
49.5 
49-7 
49  9 
50.2 

64.0 
64-3 
64.$ 
04.8 
65-  « 

|4 

gi 

67.0 

81.0 
8i.t 

fe! 

-tf 

|; 

84.0 

12  .4 
>2  7 
12  .  1 
12  .5 
12  .9 

.44.0 
144-4 
144.8 
.45-2 
U5.6 
146.0 

o 

i 

4 

5 

6 
I 

9 
to 

ii 

.2 
.  2 
3 

•3 
•  4 

5 

'.6 
.6 

4-4 

ii 

9-6 
9-7 
9.8 
9-9 

0.0 
0.  1 

26.0 

26  2 
26.4 

26.5 
26.7 

26.9 

37-2 

I 

If 
38.9 
39-  » 
39-3 
.39  J_ 
39-7 
39-9 
40.1 
40.3 
40.5 

4     2 

4     4 
4    6 
4    8 
42.  o_ 

50-4 
50.6 
50.9- 
Si.i 
5'.  4 

52!  i 
52.3 
52.6 
(52.8 
t  53-0 

102.0 

102.  3 
102.  7 
103  o 
103.4 
103.7 

124.3 
124.7 
125.  1 

146.8 
U7.» 

1476 
148.0 
148.4 

6 

j 

12 
U 

17 

4-9 
5.0 
5-' 
5-J 

~sTF 
5.4 

5-4 
5-7 

0.2 
0-5 

0.6 
«p!  8 

n't 

!if 

Ift  2 

"Hi 

18.8 
18.9 
19.1 
19.2 
19.4 
'9-5 
«9-7 
19.8 
20.  o 

20.  1 

27.0 
27.2 

27.4 
27.6 
27.7 

27  9 

!• 

6C.I 

-65.8" 
69.2 
69.4 
69.7 
70.0 
70.3 

84  6 

1? 

104.0 
104.4 
104.7 
105.1 
•05.4 
105.7 

125.  4 
I2|.8 
126.2 
126.6 
126.9 
«7-3 

148.8 
149-  > 
149-7 
150.1 
150.5 
'5°-9 

|3 

ii 

.7 

il 

«9 

20 
21 
22 
23 

•  7 

'.8 
•9 
..   -9 
.0 
.0 
i 
.  i 

.  2 
.2 

0.9 

1.0 

1.  1 

1   2 

'•3 

1-4 

28.  t 

28.  4 
28.6 
28.8 
29.0 
29.2" 
29.3 
29-5 
29-7 
29.9 
30-  ' 

53-3 

81 

54.o 
54-3 

-S44- 

54-8 
55  o 
55-3 

87:1 

|7  4 

&? 

89.0 

1* 

89.9 

1067  1 
106.4 

106.8 
107.1 

107.? 

108^2 

108.5 
108.9 

109.2 
109.6 

109.9 

127.7 
128.1 

iaS.2 

129.2 
1129.6 

.51  3 
I5J.7 
152.1 

152.5 
152.9 

.53-8" 
•54-2 
154.6 
155.0 

18 
19 

20 
21 

a* 

24 

ii 

29 

24 
29 

5-9 

6.0 
6.1 
6.2 

I  6 

M 

'•9 

2.  O 
2.  I 

70.6 
70.8 
71  i 
71-4 
7«-7 
72.0 

'30.0 
•30-3 

'3'  5 

'3'-  9 

30 

3« 
32 

33 
34 

39 
40 
4' 

3 
3 

4 
4 

4 
4 

•3 

•4 
•4 
.  5 

T6~ 
.6 
•7 

2.8 

6-3 
6.4 
6.5 
6.6 
6.7 
-67T 

6.8 
6.9 

2-4 

ii 
il 

20.4 
20.6 

20.7 

2   -9 
2   .0 
2   .2 

30-4 
30.6 
30.8 
31  o 
31.2 
3'-4 

42.5 
42-7 
42.9 
43  » 

57-0 
57-3 
.57L5. 

72-5 
72.8 
73-  * 
73-4 
73-7 

90.6 

90.9 
91.2 

?:.i 

no.  6 

III   0 

111.3 
111.7 

112.  O 

132.6 
'33-0 
'33-4 
'338 
134.2 

156.7 
I57.I 
157-5 
«57-9 

30 
31 
32 

33 
34 

35 

3-2 

74.0 

92.2 
92.  < 
92.8 

93-  1 

93-4 

94-4 
94-7 
95-  1 
95-4 

96^4 
96.7 
97-0 
97-4 
97-7 
98.0 
98.3 
98.7 
99-0 
99-3 
99-7 

112.4 
112.7 
II3-I 

114.1 

.34-6 
'34-9 
»35-3 
135-7 
136.1 
,36.5 
136.9 
•37-3 
«37-7 

I3!'  ' 

139:2" 
»39-6 
140.0 
140.4 
140.8 
141.2 

.58.8 
159.2 
IW.6 
100.0 

160.4 
1160.9 
TJTTj 
161   7 

162.  I 
162.6 
.63.0 
163.4 
163  8 
164.3 
•64.7 
165.  i 
165.6 
166.0 
166.4 
166  8 
•67-  3 
167.7 
168.  i 
168.6 

1 

39 
40 
4> 

*      ? 

3«   7 

44-0 

Il 

J9-o 
59-  3~ 
59-5' 
59-8 
60.  i 
60.  3 
_6o.5 

61   i 
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